What do you plan to grow? Are you growing plants to sell? Do they need to be ready by a certain date?
For indoor seed starting my tip is to use a soil thermometer, and know what temp your chosen seeds require.

I love the led grow lights from Happy Leaf

Edie, Cornus mas, Pinus cembra, Stewartia ovata, S. pseudocamellia, 4 kinds of Acer palmatum and a few other things that need warm incubation. Right now, I am just creating a garden from seed and growing as many individuals as necessary to have my pick of the best examples I can muster. That said, it would be great to open a nursery!!!

The building is well under way. A wooden shelving unit on casters that I was using to grow indoors is being converted to a 4 level chamber as sketched. The shelving will be skeletonized.

While I haven't checked all the best temperatures yet, the most important seeds are all 25degC. A thermostatic control already turns the heat source on and off (+/- 2 degrees).

Right now only one level is in use, but an AC axial fan is on its way. It will be ducted to the bottom and force hot air down through the duct.

The seams will all be taped. The top will have a layer of high value insulation.

But, I never know what I don't know...

Edit: I don't know what I don't know, but I know somebody's done it before me :)

It took a lot longer than I thought, but here it is! It's got two fans circulating all the air about every 30 seconds and 2 200W heat lamps for warmth. It will hold 19 10" x 20" trays in its current configuration, and it reaches 85 degrees Fahrenheit in our 60 degree basement--even before the doors are properly sealed (all the intumescent paint is outgassing again now that it's a lot warmer inside).

Interior pic. I have loaded it more than half way now. I turned out the lights (bottom left) so that the interior can be seen. The lights and fan are on different switches. Ordered another shelf for the top, so I'll be able to get 23 trays in (including the very bottom, which I am trying to avoid.)

Now that it is loaded up like this, it can get up over 100 degrees Fahrenheit. Since the temperature control unit & thermocouple wire and so on haven't yet gotten here (can't use the unit I was using with the plug-in lights) I have to keep the door cracked about 2" to keep it around 75-77

.