1. I don't consider this a contract, only a letter of understanding. It has no legal binding authority (nothing about adjudication, indemnification, remedy procedure, etc.). It falls short of being considered a contract. No, I'm not picking on semantics here.
2. What does "twice monthly" mean when the work day (day-of-week) has five days in a month? Do you do EOW, then skip for three weeks?
3. I would concur with another comments above -- trimming, blowing, and edging are optional? Don't think so.
4. If you have a rainout on an afternoon, why do you need to make contact with customer? Why any contact for a delay, unless the delay will be many days?
5. "full service" should not have a list of choices. Either you are choosing to "do everything," or you need to offer ala carte. Ala carte is not full service. Providing a choice, yet calling "full service" is confusing.
6. What is bush hogging? Maybe it is a local term, one that I've never heard. Brush hogging is a well-known term, but bush hogging ....?
7. Why would you offer a leaf cleanup schedule of the customer's choice? Either you are going to handle the leaf drop, or not. Giving the customer a choice of schedule may mean that you are unable to use methods not to your liking, or making the task more costly.
8. How can you state a price for "each and every visit," when you are unsure of what needs to be done. For example, you may trim bushes a couple of times over the season. Having the additional work may mean that your price for that visit will be different than others. Or, are you intending that these extra tasks have their charges spread out over all the payments? This may be what you mean, I'm not sure.
9. What about Sales Tax? Are you required to collect Sales Tax? If so, it should be stated clearly.
10. I'm not sure anybody would agree to your terms of no liability. If this is enforceable, then you have no need of liability insurance, right? (I would not agree to this.)
11. You mention an Invoice, but don't say how it is used. You say to send payment, or hand it to you. If this the case, then there is no need of an Invoice, right?
12. Are your late fees legal in your state. Most states have regulations on what can be changed for late fees. These rates are extremely steep, and may not be enforceable, or legal. You have no "end game" in late payments. Using your language, the $15 charges can accrue for months, or years, and yet you still have the customer.
Just my $0.02 on what you developed...