The TC should be warm.. 105F is not too hot. I measure around 40C with the disk spun down.. in 21C environment.. it is temp above ambient that is important.. so 20deg C rise is ok but you would not want more, as it will rise again during intensive backups.. it can generate a bit of heat.. but as soon as the disk spins down it should cool off dramatically.
Make sure the TC has lots of space around it.. and put it up off the bench.. use pencils or erasers or bottle tops or real rubber feet.. whatever.. get it up off the surface as a lot of heat is trapped underneath. Alternatively a good solid aluminum laptop cooler as a base to conduct away some heat.
3. this is my backup for 2 devices..., how much redundancy do we need..., do I need another Time Capsule, just in case??
You can never have enough backup and redundancy but another TC is not the way to do it.
Buy a USB drive and plug it into the TC and do backups to that.. or even better, plug it directly into each computer and use CCC or one of the other cloners and make a disk clone.