To answer your first question regarding 32-Bit and 64-Bit
Yes, its allowed and it will work
Windows 7 Retail DVDs always contain x64 and x86 versions - OEM DVDs doesn't (thx@Phillip R)Your second question about legal problems with slipstreaming servicepacks & updates
Thats also allowedPlease have also a look at the community wiki: Windows 7 Activation FAQWindows 7 Activation FAQ
It answers your first question very well
PS: I recommend nLite for those tasks
Beside your own recommendation RT7Lite you can try 7Customizer