Your battery may be your shutter problem, so I'd check that first. Also, which finder are you using? Some of the AE finders can drain the battery quickly if you don't turn the camera off after using - I always forget. I made some humorous mistakes with my ETRSi when I first got it, and a few times I thought I had camera problems when I didn't. The easiest way to fool yourself is with the shutter release button - it has a safety lock mechanism that will keep the shutter from firing. It's an outer ring on the release button - make sure it's turned all the way to the bottom (there are three settings that control three different ways of firing). I used to hate this lock until I discovered that if I left the camera on, and put it in my bag, the button would depress and take continuous meter readings, running down the battery. Now I love the lock because it keeps this from happening. Also make sure your mirror lock and double exposure switches are in the "off" position (Saint Butkus has the manual here: http://www.butkus.org/chinon/bronica...nica_etrsi.htm). And since the shutters themselves are in the lenses, see if you can duplicate problems with different lenses. It's a long shot, but it could be a lens. Make sure you test this without the teleconverter.
Hope it's something simple!

As far as older lenses and backs go, it's like everyone says - they all work. BUT, I find that the newer backs and inserts work much better. If you're shooting color you can usually get 220 backs cheap at KEH, and Kodak still sells Portra in 220 size. Have fun! I love my ETRSi, and it can deliver incredible results.