Electric baseboard heat is cheap to install. Is is expensive to use? Depends on your kwh charge. For me in Manitoba with a plethora of hydro generated electricity it is cheaper than natural gas. If you live anywhere where the generation is of a thermal nature, as in coal, oil, or gas burning, it will be expensive.
Yes, you need dedicated 240V cc'ts. Baseboards are hard wired. Yes, you can run the cable through sheetrock direct into the heater. They have their own integral junction boxes. If you want to be able to turn them off entirely when not needed, use double pole thermostats. Otherwise, you'll need to shut them off at the breaker. I'd recommend wall mounted T-stats; much easier and responsive than the heater mounted T-stats.
Brands of baseboard? I use the cheapest from the big boxes. They're cheaper there than the electrical supply houses.

I've installed and used electric baseboard heaters in several environments and I'd ditto everything that bigbird wrote.

I'd especially recommend using one or more double-pole thermostats. If the total amperage requirements work out (say not more than 25A @ 240VAC or so), you can probably use a single, inexpensive thermostat. That's the most convenient solution, since you won't have to run around trying to sync-up or "balance" several radiators.

To guestimate your capacity, it'd be helpful to have an idea of how large an area you intend to heat, whether you'll have insulated walls and whether there are windows, walk-out doors and/or uninsulated, above-grade exterior wall segments.

I have electric baseboard heat installed in my 24' x 32' detached workshop in Virginia, and since oil prices have risen so drastically in recent years, I've concluded that my shop is now a good bit cheaper to heat than my house (oil/hydronic) on a cubic-foot basis.

From the perspective of planning the wiring, one thing I'd keep in mind is the restriction against placing receptacles directly above baseboard heaters. You can use outlets that are integral to the heaters or you can tailor your placement of baseboard segments so that you can have normal in-wall receptacles where you really need them.

Just a thought...

In my experience, one brand of baseboard heater is as good as another. Most situations work well at 10 to 12 watts per square foot of floor area. It is now more difficult to find heaters that are "high watt-density". That is 300 watts per foot of length. Medium density heaters are 250 watts per foot. So a high watt-density heater 8' long would be 2400 watts while a medium density heater 10' long would be 2500 watts. The medium heaters give a bit better distribution, but eat up more wall space. I prefer the high density units. Use a separate thermostat for each heater unit if you wish. Do not put a wall thermostat directly over the heater. Thermostats mounted in the heater make for easy wiring, but also give the poorest temperature regulation.

Thanks!!! I would have never known about NO outlets above the heaters. I will certainly add that to my design.

In regards to your question...the space to be heated is about 550 square feet. In regards to exterior walls:

There is one wall that is 18 feet long and below grade (I just installed 1.5 inch Owens pink basement board, and may cover that with unfaced batts).

The other exterior wall is 27 feet long and is a walk out basement wall, so it is "above grade." On this 27 foot wall, there is one exterior door and one 50x97" inch long window. I will frame this wall and insulate it, as well as replace the old window and door. The other 2 walls in the room are bordered by the furnace room (uninsulated), and some small rooms that border the garage. Undecided what to do here, but I guess these can be considered uninsulated. The doors are always shut, so the room I guess provides the buffer zone. The rooms are always colder so the doors we keep shut.

Glad to hear you'll be insulating. That'll certainly help. I'd consider the walls bordering the furnace room and those other rooms to be uninsulated, although it still helps that they are interior walls and the presence of the furnace may help a little.

I forgot to ask you about the climate in your area, but judging from your screen name, I'll guess New York. Still, there's quite a bit of difference between Long Island and, say, Syracuse or Buffalo. (I know--I went to college at Syracuse and remember feeling colder there than at my farm in Maine!)

My seat-of-the-pants guestimate (and take this as precisely that, no more!) is that you can probably heat this space with a minimum of about 22' of ordinary electric baseboard (one 6' and two 8' segments, for example, with other configurations possible) for a total of at least 5,500 watts. (Make sure to check the actual amperage/wattage ratings of the heaters, though!) Unless you're in a warmer climate than my assumption, I wouldn't go any lower than that.

This sizing should permit wiring on a single dedicated 30A 240V circuit with #10-3 wire, which makes for about the simplest of approaches. I recall buying an inexpensive double-pole thermostat at Home Depot a few years ago that was rated for 25A total loads, so I'd think you'll be able to find one in the $40-$60 price range, although I haven't spent much time on that aisle in a while. (I could be off on that.)

As for placement, I'd make sure that at least one of the 8' segments is placed near the walkout door, and one on the other exterior wall. The third could go on the other side of the door or an adjacent wall, depending on your dimensions, anticipated traffic flow, etc.

When I say "near the door", what I'm suggesting is that you wire a receptacle outlet close to the door followed by the baseboard section and then an outlet past the other end. This would maintain your outlet spacing such that there is a receptacle outlet within 6' of any point on the wall. (That's an abbreviated version of usual code requirements for minimum placement of receptacles.)

As bus driver noted, you'll want to place the thermostat(s) well away from any of the heaters.

Are plug in oil filled radiators electric heaters better than baseboard ones? Do they make oil filled baseboard also?

Oil filled is not at all more efficient than other types, nor less so. Waste of money, in my opinion.

The plug-in ones are easier to do than hard-wired baseboards, but you will prolly need several of them to make the space warm enough, and they wont' do a good job of spreading the heat out. You would also need to wire your outlets accordingly, as two of these units pluged into the same circuit may trip the breaker.

The other consideration is that without permanent heat installed, you can't call the space "heated".

Since this is a cellar, I would suggest using less Wattage than the rule of thumb. The "outside" temp will not fall as far as it will above grade.

When I finished a cellar years ago and used 10W/sq ft of baseboard heaters, I found that the heaters tended to short-cycle and overshoot the thermostat setting, causing too much of a temperature window. When the thermo was set for 68 deg F, the room would sometimes get as warm as 72 deg AFTER the thermo had shut down the heaters. Then the thermo would not restart the heaters until the temp fell to around 66 deg F.

Cutting the installed Wattage by about one-third increased the heaters' duty cycle, and narrowed this range. That improved the comfort quite a bit.

In this old house I have a cold upstairs room - it has no heat register for the central furnace - and I heat it with a baseboard unit. It's a second storey room and the insulation is pretty mediocre - only what fits between the roof rafters. W/O the BB it is typically 10-15 deg cooler than the rest of the house in winter.

I'm using 7.5W per square foot and it works pretty well. I'd suggest that for your situation. You can always add more capacity if you need to.

How you maintain outlet spacing on large sections of heaters...can the outlet requirement be "relaxed" for electric baseboards?