I have a tall DS5. We first took him to WDW at 3 years and 2 months. He was just over 41 inches tall. He loves Splash Mountain to bits, it's his most favorite ride ever. We usually have to go on it multiple times. We made sure he knew about the big drop, we let him watch people coming down it. He didn't have any problem. We did the same thing for Test Track, and he loves that too. The thing he hates about TT is if we have to queue! BTMR wasn't open when we went the first time, he does enjoy it, but not nearly as much as Splash. Goofy's Barnstormer is a big hit too, it's a very short ride, you can see it completely so you can both look at it and decide if it's something he might want to try. Kali River Rapids over in AK is a bit wild, in that you get drenched, but again my DS loved that at 3. He is tall enough for Space Mountain nowadays, but the seating configuration (he would have to sit on his own) is not something I am 100% happy about. I think that would bother him...well probably me more, but you get the picture! The rides he doesn't like are the ones that are dark and loud. He is not a fan of The Haunted Mansion.
I am super over protective, so I do understand your concerns. If you aren't confident on taking him on any of these rides, then don't. He will have a perfectly good time without them! More time for hugs with Mickey!
