Automated Lawn Mower - Project Idea

I had an idea of trying to automate a ride-on mower. I know this will be tricky to do but I am up for the challenge. But since I am still very new to the whole Ardupilot thing I am going to need some help throughout the project and also at the very start of the project. Which leads me to my first question. Since you now know my idea what pixhawk would you recommend for the task and why that one. Also if you have multiple recommendations for different reasons I am open to reading them. I was also wondering if someone that might have played with rovers before would know what else I would need to make this project successful. Because with trees in the way I probably would need something to sense that and dodge them and the same with maybe the roots that are in the grass from the trees. Also maybe I might need to set something up in order to get more accurate in movement around the backyard. Thanks In advance and I am sorry if I do not reply very quickly.

Several people have already done autonomous mowers with ArduPilot. If you search on this site you should be able to find them.