Hi and welcome... first off 25/16 maybe a bit hard, "normally" a 22/16 - 22/15 gear ratio is used on 24" bikes. As for longer stem, if you lower back feels "too bend" maybe a higher stem or a handlebar with more raise is better. If you are hitting the knees a lot on the handlebar, maybe a longer stem. As a rule of thumb: Always make your bike setup comfortable when standing on the bike both wheels on the ground, if it feels wierd or hard standing on the bike, modify it a bit. Good luck and have fun with it...If you need more help on bike setup a pic of you on the goat...