@David Fairall, I agree with @Brian Sparr. Very good advise. Do you have very much construction experience? I think you can find a good electrician to change the outlets to GFIs without too much cost. Windows can be pricey for someone to install. My husband and I changed all the windows at a property we owned last year. The actual cost of the windows was a lot cheaper than I had expected and we were able to remove and install them ourselves, which saved us a lot of money.
I would only replace the sprinkler heads that aren't working, and I would really consider putting a timer on if at all possible. My experience with my homes is that the yard gets seriously neglected by your tenants if you are not around. Anything you can do to make it less work, will benefit you in the end.
I would consider painting the house the same color. Paint doesn't cost too much and can make a big difference in the overall appearance and feel of the house. Plus, it is nice to be consistent as you acquire more properties and not have ten different colors you have to keep on hand.
The kitchen and garage door are a little harder to decide because they will cost you the most. I have really old cabinets in one of my rentals, but we painted them inside and out and updated the hardware and they turned out pretty nice. I would consider that before completing a costly kitchen remodel. That same rental also had a old wood garage door. We finally ended up replacing it with a new door and motor last year. The new garage door is pretty awesome and quiet. I would probably wait to do it until later when you have more cash flow/month.
I would trim trees and just clean the gutters more often instead of investing money into that issue. I bet they just hadn't been cleaned out in a long time and cleaning them out once or twice a year will probably solve that problem.
Not sure how helpful that is to you, but I wish you the best of luck! If you are someone that likes projects like my husband and I, then you will probably end up doing all of these items just to have something to do! Good luck!