Been there, still trying to do that...
I have been doing a multitude of services for many years now. It's not a good plan. Unless you are making enough money to fund a full effort, stay away from the tree work. Reasons:
1. If you are going to be doing the work yourself, the specialized equipment necessary to be competitive will be sitting around unused a good part of the time. This is real expensive for high priced items like chippers, grapple trucks, bucket trucks, etc. You take the time to go do tree work, landscaping equipment sits idle... You go take care of a landscaping project, then the tree equipment once again... sits idle. This gets expensive.
2. Unless you are pretty good at managing people, it will be very difficult to keep employees capable of humping logs all of one day, and then exercising the necessary finesse to plant flowers or lay bricks the next day. Put the guys that are good at running lawn equipment on the end of a chainsaw, and you will be sharpening a lot of chains. If they are used to mowing grass, they will quit when you ask them to tote 80-150lb logs all day long (or worse, they will just. go ..slow...all...day....long).
While it is easy for nearly any ambitious, dedicated business owner to acquire the skills to do many jobs (that's me!), it is damn difficult to find employees with the same set of talents (this is my biggest failing). You are much better off if you can get specialized people for each task. This predicates having enough work to keep employees for each specialized function working full time.
3. It doesn't sound like you have much experience in tree work. It is VERY hard work, it's dirty, and it's dangerous. Workers compensation expense is out of sight ($$$), particularly for a start up company. Experienced help that will actually come to work predictably is difficult to find. The good ones are already working for a better company than yours, or they are working for themselves, doing what they like to do best.
4. Your original post sounds like your primary motivation is to make good money. Take a good look at most of the tree services that you see driving down the road. Go to the local log disposal site and look at the kind of equipment that dumps there. How many of them look like they're rich? While there are some companies that do quite well, most of us are struggling just to get by.
My suggestion: If you want to work for yourself, form a business plan that makes money at what you know BEST, or at least plan on making a living at what you LIKE best. When you find that you are rolling in the dough, your company is growing by leaps and bounds, and you have the capital to invest in a new division/PITA: go for it! Until then, I predict increased headaches from trying to do something that you are ill prepared to start.
[In my experience, landscapers and lawn workers generally make poor tree crew members. Conversely, the tree workers don't seem to do very well in lawn maintenance and landscaping either. I've been doing both for over 25 years, and I still haven't mastered the trick of managing people into being both good at tree work and good at landscaping and grounds maintenance. So...I do poorly at two trades rather than well at just one. I don't know of any companies in my area that do well at both, either. Oddly, my tree climbers invariably make pretty good tractor operators... go figure.]