First, a lot depends on where you are. I'm in Oklahoma so there is a long growing season. I usually start my plants late in April to get them out in early may. (Remember the days are shorter so your indoor lighting should be about 14 hours on to keep them from going into flower when you put them out). I plant in the ground, not in pots.
It's never too late to amined your soil, but it's best to get it ready in the fall. I start with a hole 4 feet diameter and 18 inches deep. The hole is refilled with the 1/3 soil, 1/3 compost, and 1/3 manure. Do side dressings thru the grow of compost and manure.
Most of the problems that I have seen are caused by people feeding their plants. There's nutrient burn and deficiency. Stay with organic and in the the ground and those problems mostly go away.
Pest control is easy enough if you pay attention to your plants. My total pest control is first: Keep the plants clean. I like to hose them off maybe once a week early in the morning while the is still dew. Second: Spray once a week with soapy water and then with BT.
One major thing is don't try to love them to death. They are plants, just like you tomatos. That's about how much attention you should give them. Just keep them fed and watered and the bugs off.