If the only reason you are thinking of getting an RV is due to the cpap, just know that many tent campers have battery setups for that. You don't need an RV to camp with a cpap - just a battery that can run it through the night and a way to recharge it the next day (generator or solar). You can find examples of setups on many tent camping forums.
If you want an RV for more than the cpap, then I suggest you consider what you want to do with it. For some, RVing means sightseeing and traveling. For others, it is simply camping off the ground. And for others, it is a combination of the two. Knowing how you want to use it will help you decide what you really need. Understanding that will help you wade through a lot of the suggestions and recommendations offered.
For example, if you will just be camping off the ground, then a toad is likely not necessary (unless you tend to drive to distant trailheads for hiking, etc).
If you plan on sightseeing and traveling, then where you choose to stay will make a difference. If you stay at RV parks with hookups, then you don't need to worry about battery size because you can run the cpap off shore power. If you want to stay at dry (no hookups) campgrounds, then the battery size is much more important.
Once you know how you'll use the RV, you can better decide what will work best.
Size of the camper will get a ton of comments. Some folks believe in getting the biggest possible. Others want the smallest. My class C is 21ft and works great for me, two dogs, two cats, and a parrot. A friend has a sunrader class C - it is on a toyota chassis, so is smaller. Its size better allows her to drive into cities, etc. If you stay at RV Parks, size won't be limiting. If you have specific campgrounds you enjoy, size can make a difference.
Fresh water and holding tank sizes are also a consideration. Again, if you stay at RV Parks, you'll have hookups, so it won't matter. But if you dry camp, then it is a bigger consideration. My clipper has a 40gal fresh tank and 20gal each grey and black. I can go two weeks (using campground showers) without needing to dump or refill. In contrast, my folding trailer has a 20gal fresh tank (holds about 18), a cassette toilet and a 20gal grey tank. The clipper works great for traditional camping because I can just go and not worry. The trailer works well for sightseeing/travel because there are usually facilities to dump and refill nearby or I can overnight at an RV Park between stops.
1975 American Clipper RV with Dodge 360 (photo in profile)
1998 American Clipper Fold n Roll Folding Trailer
Both born in Morgan Hill, CA to Irv Perch (Daddy of the Aristocrat trailers)