IME when to start with garden tasks will vary considerably year to year. Some years we still have a couple feet of snow at this time of year, and other years we are in the middle of mud season when the ground deeper down is still frozen and melting snow creates a surface layer of mire that sucks off one's boots. Rarely is it this clear and dry at this time of year here in coastal NH. I have done some raking, though gently in very well-drained areas. We don't fertilize the lawn (just mulch leaves and clippings back in), so I can't help there, but you may need to lime it since our soils tend to be more acid than lawns and veggies like. Have a soil test done to check.

As far as trees, shrubs, and perennials, often what is sold here has been grown farther south, so if it is newly leafed out, it can be frost damaged. If it is not leafed out or is evergreen with buds not yet opening, it should be fine to plant when the ground can be worked, mostly a matter of drying out enough. Soil tends to be acid, so ornamentals that like that will be happiest. Glaciation has had an effect on our soils, so many tend to be poor in organic matter, so you may want to put some energy into improving planting beds if the previous owner wasn't a gardener. Plants do better if the entire bed is improved rather than just the planting hole, especially for woody plants. Depending where you are exactly, you may find the soil is extremely rocky.

Being at the coast, you will have warmer falls and cooler springs than inland since the Atlantic is a huge heat sink, taking longer to cool and warm than the air and ground further inland as well as much more breeze year round. Here are the average last spring frost date and average first fall frost date maps for Maine. Remember that these are averages, so you should wait at least a couple of weeks after this in spring to plant frost tender plants. Often folks suggest Memorial Day. Both maps are zoomable, and here's a similar zone map.

You may find useful info from the UMass Landscape Message under the North Shore since it's not far from southern Maine. Just add a week or so to the timing. Click on the current message, and then find the link for North Shore, which is coast, north of Boston.

Maine Cooperative Extension also puts out a newletter, Maine Home Garden News with the links for current and past issues farther down the page.

For inspiration, there are some really nice open garden days in York, ME and Portsmouth, NH most years. There's an azalea garden that's open to the public somewhere midcoast (Rockland/Camden area perhaps), the Coastal Maine Botanical Gardens, and Bedrock Gardens in Lee, NH.

I'm a bit South of you, in Zone 6 Massachusetts. Here, April is the perfect time to plant dormant bare root trees and shrubs. Lots of people end up doing it late. Be wary of any shrub that is INSIDE of a Home Depot...it won't be acclimated.

If you are in Maine and new to the area, I recommend you look into the

New Hampshire State Nursery.

Main concern for raking and planting dormant trees is whether the ground is still too muddy.

Annuals you should wait for a while.

I am about 1-2 hours south of OP and I would also suggest Memorial Day to be safe. I always WANT to go all-in but May 1st but it's not warm enough for heat-loving plants so Memorial Day it is!

It really depends on what plants we are talking about. Some should have been planted last week. Some can't be planted until June. Sort of like the way I turn the heat down when we go away for the weekend. It is too cold for humans, but the cats in their little fur coats like it just fine. Then there was my sister's Keeshond who thought zero degrees in a blizzard was a fun place to be.

There are an assortment of maps. Average frost dates are useless. The usual measure is 90% - 9 years out of 10 the target temperature doesn't happen later than that date. For most annuals, the target temperature is freezing - 32F. For actively growing hardy perennials, shrubs and trees the target temperature is around 28F. For dormant shrubs and trees, they can be planted any time the ground can be worked. The sooner the better so they get a chance to grow roots before things warm up.