Way to go!!! Sounds like you need to update your compression tester. I have one from harbor freight that has several screw in adapters for various thread sizes, and a hose that leads to the air pressure gauge. Can't remember exactly how much it cost but it wasn't excessively expensive. Getting an accurate compression reading is essential to determining what kind of work may be needed i.e. valve adjustment, etc. As long as all 4 cylinders are within around 10 - 15 psi of each other that should be good enough to run OK. I think accepted is within 10 psi but a little more of a variance is no real big deal.
Getting the carbs rebuilt properly and correctly sync'ed is the next big thing. There is an excellent video available on ebay about rebuilding VMax carbs but the Venture is the same, just a little different on the jetting.
As far as spark plugs go, NGK is an excellent choice, and should only run 2 - 3 bucks per plug. The Irridiums will last a little longer but to just plain get it running just get the regular ones...