For my money, Win 7 Pro 64-bit would be the choice.
Windows 8 will drive you mad whether you have a touchscreen or not.
You need 64-bit for any memory usage more than 4gb anyway (otherwise it just sits there and can't be used by the computer).
4gb vs 8gb - depends upon what you're using the computer for. e.g. if you're using it to browse the web, write the occasional word doc, the odd spreadsheet, etc then the 8gb upgrade would be a waste of money. However if you do a lot of video or photo editing or fancy yourself as a CAD engineer then 8gb would be useful.
Cheers,
Mike.