Knuckles has a decent base speed and a better handling/turning ability than sonic out of the starter characters (Turning ability is quite important, because drifting and counterdrifting is faster than just running straight). He also has the glide ability which helps you on the Saturn version a lot as you only play on clear weather so you wanna dodge all the water. The route you described is fine and you should practice everything the way you would do it in a speedrun (so yes practice both with knuckles and super sonic). Loops on the saturn version are weird in general as some rings in loops are just not collectable, could also be due to rubberbanding/catch up as the CPU speeds up when you are further ahead to make the race closer. If you have more questions it would be best to ask them in the Sonic R Discord if possible as we are more active over there. The pinned thread by daily has the invitation link if you are interested.