In all seriousness I would make sure you are covered for heights over 25'. Your underwriter may think trimming is ornamentals and pruning is mature trees. Either way I would read the fine print to make sure you are well covered. I usually have these things reviewed because I am not an insurance expert and I don't have the time to become one.
You can do as many businesses as you want. If you've read Good to Great by Jim Collins you know that it is not what you can be good at that matters. What can you be the best at in the world (or at least your local area). If you concentrated 100% of your resources on landscaping, tree work, lawn care, etc., you would most likely be more profitable. There is a point where repetition produces efficiency. The more you do something the more efficient you become at it. This doesn't mean you can't make money in trees, building decks, cleaning windows, etc but it does mean most companies are most profitable when they are very vertically integrated.
Lawn care/landscaping takes different equipment and skills than tree work. There are some parallels but I'm sure I can clear an acre of trees more efficiently than you can. I'll bet you can take care of an acre of landscape/turf more efficiently than I can. It comes down to equipment and experience. I'll make more money on most tree jobs than a landscape company and vice versa for landscape jobs.
I agree 100% with this. I am often asked why work the day job? The answer is I am good at it, it pays well and there have been more than a few times I was happy to be sitting down at my desk on a Monday morning. It sometimes feels like I go to my day job to rest.