1) Film holder issue: It is pretty easy to check the "new" vs. "old" film holder issue. If the back comes off, remove it and from the inside (ie the side of the ground glass that will face the lens), check the depth from the face of the wood to the ground glass. Easy way is to use a straight edge lying corner to corner across the back then take an unsharpened pencil or other small cylinder and check the depth a few places along the straight edge. Make a mark on the pencil for reference. Then insert a film holder, remove the dark slide and check again. Granted, if everything is perfect, you will be a hair lower to the holder's septum since the film isn't in place. But if you are noticeably different in depth, PROBLEM. You will need to figure out how to shim the glass or holder.
2) Lens issue : lots of relatively inexpensive barrel lenses go by every day on eBay. With slow film and if you have a small apeture, your exposure will be in seconds anyway. Lens cap or a hat becomes your shutter. In the mean time you can make a lens board to hold a pinhole and experiment with that. You won't be able to see much (if at all) on the ground glass but you can use the camera. A good check for light leaks in the back and bellows too.
Third thing, while you are fooling around, consider using a piece of 8x10 photo paper (trim it a little bit to fit the holder) instead of film. Much cheaper and you can practice loading, unloading and processing your "film" with a safelight. Best guess for the average piece of RC VC paper would be an ISO of 5 to 8.