Reusing parts for a pc build

[UNDRCVR]

I am re-using parts from my HP Elitedesk 800 G1 TWR (cpu, cpu fan, sshd, optical drive, ram) to build another one with an MSI H97 PCmate and a new powersupply and case. However, my current pc is a windows 7 downgraded from windows 8 pro and I do wish to operate in Windows 8 pro on my new pc because it sounds cool.
1. What do I do to ensure that I can reuse my sshd so that the OS is safely installed?
2. Also, my old cpu fan does not fit the new board :/ (theres no backplate for the motherboard as the old pc case acted as a support for the cpu fan and the holes in the MSI one do not align with the screws). What cpu fan should I get then?
3. I decided on a dedicated graphics card, the zotac gtx750ti but will it be compatible with MSI motherboard even if it physically fits it?

I am so so scared ill screw up because its my first time

 

[CountMike]

If you are sure that CPU and RAM are compatible you could use either standard CPU cooler or some aftermarket one. Standard one comes without back plate and aftermarket ones include it in the kit if necessary. If everything fits in the new case, you'll have no problem with gtx750ti.
As for SSHDD, it should work too but you may have problems with windows. It may not BOOT at all and there might be problems with drivers and certainly with activation. Best course would be to do clean install of either W7 or W8 if you have retail licenses for either or both. Another option is to go to Windows 10, it is but improved version of 8.1 anyway but has some features (Start menu) of W7. If your W7 or 8 license is retail, you can activate 10 using registration for one of them. If you want 10, you'd have to do it before July 29th because that's when free upgrade offer expires.

 

[UNDRCVR]

If you are sure that CPU and RAM are compatible you could use either standard CPU cooler or some aftermarket one. Standard one comes without back plate and aftermarket ones include it in the kit if necessary. If everything fits in the new case, you'll have no problem with gtx750ti.
As for SSHDD, it should work too but you may have problems with windows. It may not BOOT at all and there might be problems with drivers and certainly with activation. Best course would be to do clean install of either W7 or W8 if you have retail licenses for either or both. Another option is to go to Windows 10, it is but improved version of 8.1 anyway but has some features (Start menu) of W7. If your W7 or 8 license is retail, you can activate 10 using registration for one of them. If you want 10, you'd have to do it before July 29th because that's when free upgrade offer expires.

So to do a clean install I wipe the sshd and then go on with installing as per normal? I have the discs for windows 8. And what do you mean another option is to go to windows 10?

 

[CountMike]

Clean install is preferable. You could install W10 using registration for your W8. It's free to upgrade from W7 and W8/8.1 until July 29th.