If you build it, they will come. Now if you want them to stay... build WIDE lots of 40 feet or more.
Try to make the spots level with terracing if need be. Leave as much to nature as possible.
I've stayed in several RV parks that also had a mobile home section, so the fact there are two mobile homes already wouldn't be an issue.
If you can offer Wifi and Sewer as well as elec and water, you will likely stay very busy. Also keep the dog rules simple like SC State Parks.
Figure out how you are going to handle the garbage. One park I stayed at, the owner drove by everyday in his pickup truck and picked up the garbage from each lot then he stored it in a dumpster away from the campground. Another one just had 55 gal outdoor garbage cans scattered around with liners and they emptied these daily. Seems they only had one can per 6 lots, but I never saw them overflowing.
I wouldn't worry about being close to amenities, most RV's have room enough for plenty of groceries. People that like to stay with nature in the boonies (like me!) are used to stocking up ahead of arrival.
Good luck and let me know when you open, I will come.
I have stayed in a "back yard" RV camp. The guy had built 4 large spots behind his house for RV's with full hookups and then he also had set up tent camping in the woods, with a car park area for the tent people. We were the only RV during our stay, but he was plenty popular with the tent crowd. He did build a shower and bathroom on the rear of his house for the tent folks to use.
I've stayed in several RV parks that had sewer hookups and no bathrooms or laundry. So you can pretty much design your RV park any which way you choose, just be honest about it when you put up the website so folks know what to expect.
All lots do not have to be identical either. Many parks I've been to have erratic sized lots scattered around trees and nature. You might get a large one, you might get a small one, just be honest about what maximum sized rig will fit in each lot.