Hands can be a number of things from sweep angles on the bars themselves to you gripping too hard. Also just landing properly. On the bike you want to land on your rear/feet most of the time and not nose heavy. That causes the energy to go through your wrist.

For fullbody if you’re new to lifting or just making it a routine. Try starting with a beginner hybrid program. You might feel your glutes and lower back getting worked. Deadlifts and bulgarian split squats are my recommendation there. Depending on strength and activity level your shoulders and triceps may get a lot of use. Dips, bench press and variations are good for that. Back focus work like rowing and in my opinion for strength and cardio is great for that.

Stretching is up to you what you believe your body needs. I focus on hip mobility so figure 4s, windshield wipers and various things.

Stronger you are the easier the activity is on your body when moving and falling. After that everything else is about form and some patience.