I do not think you would have any problem. It has been a very long time since everything supported 64 bit operating systems.
A 64 bit os is only of value if the laptop will have more than 4gb of ram.
Have you considered using a SSD? I have changed out all my laptops t using a SSD. It absolutely transforms the performance.
As to drivers, you need to look at the HP web site and find the appropriate drivers. If you don't see 8.1 64 bit drivers, try w7 or even 32 bit drivers. They will mostly be needed for hp specific hardware like trackpads