The size after installing is nearly the same for ALL versions of Windows 7!! That means that you've to remove other apps/data from your HDD for to free up space!!
Yep, with a small SSD like that, your limited to just the OS, future updates and a handful of small programs regardless of the version of Windows you install.
80 gig's ----- I would not even use half of that. I have a 200 gig drive with s partitions on it with 3 operating systems. 2 XP systems and one Win7. First XP and Win7 have the same identical programs on them. The second XP does not have much and just use it for testing things. All systems are fully up to date. Of the 200 gig's I only use 38.7 gigs. But then again I don't save anything on that drive. Everything is backed up on externals right away.
I've been running 7Pro 64 on an Intel 40g ssd for years with no problems.. get yourself an external HD for your big files and backups ,turn off your page file and be done with it