Actually you could have upgraded to W7 64-bit, every upgrade from XP to W7 is a custom install and upgrading to 64 bit works the same as 32. And just FYI, with a W7 upgrade license you can simply use the double install method rather than reinstalling XP first; you simply install W7 twice and activate after the second installation.
If your upgrade license is for the Ultimate Version then, yes you can install the 64-bit edition now but you
may be asked to call Microsoft to activate again since you already recently activated. And yes you could go back to 32 but, again, you may be instructed to call Microsoft to approve the activation.
As for Windows 8 upgrade you probably don't have to have win7 Installed either, you might check out this thread on a Windows 8 forum
HERE and see if that works for you (NOTE: that forum is not related to this forum).