As RRH said, a lot of questions. And he gave you a lot of good advice, the best in my opinion is to contact your local county extension service. I'm sure access to such things vary, but in my area several of the independent nurseries and even one of the feed mills work direct with the extension service which ultimately work with one of the state universities, so you can drop off a few soil samples and receive a very comprehensive report full of advice specific to your property. There are a lot of types of grasses, and most seed that you buy will be blended to some extent, but the bottom line is that grass needs sun. So, as far as your front yard, I would first look at the possibility of trimming some of the trees to allow at least partial sun. In the middle of our front yard is a large red maple, under which the grass was slowly disappearing, the bare spots creeping out a little more each year. Last year I got a bit more aggressive, removing a number of lower branches, thinking that I will reseed it at some point, but some of it is already filling in itself this year. Now, I'm not sure how much of this is actually relevant because I'm not sure if you are saying that you want to tackle any of it or if you're wondering what a lawn company will do. If the latter, you will have to contact a few in your area and see what they recommend and offer, because you want one good plan, not two; you don't want someone else to come in and do one thing and you end up countering or doubling up on their activities. Not that you can't still assume some aspects, but fertilizing and killing weeds are pretty much either/or.