I meant to mention that the tractor can't harvest money trees. I've never noticed any problem with them being harvested "manually" on farms with the tractor though. And I've had the Swift Gro on that same farm, so not sure what happened there.
As for the number of plants; I have a pretty powerful system, so I haven't run into any problems with a fully planted Grandpa's farm. When I bought my system a couple years ago, I threw a lot of money at it to make sure it could handle Sims 3, since it is primarily what I was buying it for. I'm glad that I had the opportunity at that time and have never regretted it. The good thing about playing a retired title is that I know the specs aren't going to change. If my system can handle it now, it will still be able to handle it three years from now.
That is, as long as MS doesn't go messing with Windows 10 too much. My laptop warranty expires in January. At that point I'll be able to start playing with my system and I think I'm going to create a second boot drive with a full Sims install and keep that drive from any future online updates. After that, no matter what MS does, I'll have a compatible OS.