Take hard drives with you, no need to replace them unless you want more space.
Windows may transfer over but if OEM key likely won't activate on a new board however there is certain places you can source windows keys for few quid.
What's your budget for the board and CPU?
Certainly would like at getting the Ryzen 3600 at least mind
Mark what CPU can I get away with on my board?
Budget wise wouldn't want over £500/550 for board and cpu.
Ok so that's great about hard drives so I can just change them onto new pc. Do you think I woukd have to get a new tower or doesn't it matter. This is 2nd build so I'm unsure of how it works with upgrading.