I have a few recommendations for you:
First, re film holders, I checked my Sinar catalog for Normas from when I bought mine new in late '60s. It says the back accepts both 4x5" and 9x12cm film holders, although the 9x12 holders must obviously be different so as to accommodate the 9x12 film. You should use 4x5 film and get some used 4x5 holders, which sometimes appear in the APUG classified section, but very frequently in the Large Format Photography Forum (which you should register for - it's free
here). There's a wealth of info there for both beginners and experienced, but you must be registered for one month before its classifieds can be used. At that time, I'd post a Want-to-buy (WTB) ad for holders; they can be had for +/- $5 each.
Next, re the Symmar: It sounds like your shutter could use a CLAC (clean/lube/adjust/check) by a reputable technician. Many from the LFPF forum use Carol at Flutot's (
http://www.flutotscamerarepair.com/); she's very experienced with all shutter types and the website offers some useful information on shutters. I have a 360/5.6 Symmar in a Compound shutter that she's fixed up for modest cost. There have been times when her backlog gets sizable and you may have to wait a bit, but it's definitely worth the wait. My Symmar has also developed some "haze" in the rear cell, and after some research I concluded that it's due to the onset of separation of internal elements rather than a fungus - which has an appearance all its own. It's not too severe so I've decided to continue using it and avoid backlit subjects. Regarding the "spots" you see in your lens, it's very likely a condition known by many LF'ers as "Schneideritis." It appears as many little black or white flecks inside the lens cells - it doesn't seem to have any effect on image quality, but it does affect resale value. So I'd suggest you continue to use the lens after getting the shutter working ok.
Finally, I recommend you get a copy of "Way Beyond Monochrome, 2nd Edition", co-authored by Chris Woodhouse and Ralph Lambrecht (an APUG member). It's the best up-to-date photography publication I've seen. Look
here for the hardbound copy. Worth every penny. It also contains instructions for building your own shutter speed tester, a pretty simple device that I built rather quickly and have checked all my shutters at all speeds, then put labels on my lensboards for any corrections needed.