I know just how you feel, i bought a Jawa 350 off ebay in february...
pics werent very good, had no idea what the bike looked like, if it turned over, if it was complete, description was very short, won the auction for about £150.
went up to swindon a few weeks later with my dad to pick it up in the van, met the bloke in sainsburys car park and he wheeled it out of his van, flat tyres, paint peeling off, flat battery, carb hanging off, covered in dust, rust and sh*t. put it into our van, paid and went back home to newbury.
first week or so was trying to get it running, having only been riding 3 months and having literally F/A experiance with engineering and motors i didnt know what i was doing, a seal was missing in the carb which meant the bike would not run
i still got that Jawa, it now starts first kick every time and runs very well, i have since sealed the carb up and needs only the exhausts sealing up, new rear tyre and new alternator brushes to get it tip-top again.
always keep positive, first stage is getting it running so sort that out first and then you can start thinking about what to do with it in terms of tidying it up. usually once you hear it fire up for the first time it gives you a reason to keep working on it.
clean up what is rusty and re-use what you can, if it is something simple like a gasket then make it, don't start buying new parts unless it is really essential to the running of the bike.
its all a learning curve, just for some it is steeper than others