Hello,
I am CPU mining at around 100H/s on my home computer. I have three questions please:
1) CPU temperature is getting to around 90°c. Am I damaging the CPU and hugely reducing its life expectancy doing this?
2) Could someone please give me a rough estimation as to how much power this is using? I always left my PC on anyway..
3) I also have a little fleet of PCs. Is there any device which connects to my mobile phones 4G, then can act as a access point for many PCs and use my mobile phones 4G for internet access? my phone only allows 3 connections

Thanks
1) that's far too hot for any CPU - you need to improve your cooling. Check the brand of your CPU, confirm which socket it uses then buy a new heatsink/fan combo (also check the height of your case)
2) You can use a device like this:
https://www.amazon.com/P3-International-P4460-Electricity-Monitor/dp/B000RGF29Q (which will tell you how much the whole system is using)
3) if cellular is your only option, I would do this:
https://www.amazon.com/TP-LINK-TL-MR3020-Wireless-Portable-Router/dp/B00634PLTW. get a new sim card or add a data sim card to your existing plan