I know that there can be a ton of factors that go into whether one currency appreciates vis-a-vis another one, but it seems to me that one of the biggest factors, if not the biggest factor, in the very long term would be how much money are their respective governments printing. If one government is printing an amount equal to 5% of its GDP annually, but another is printing 100% of GDP annually, I just think it would be very tough for the ladder to do anything but depreciate vis-a-vis the former over the long haul. Am I thinking about this right? Have there ever been any studies on this? Thanks!
There is more to it. Your numbers are not realistic. If a country is issuing debt at a rate of 100% GDP then it is financing any and all of the growth occurring and debasing the currency. When we say "printing money" generally speaking this refers to debt monetization. The central bank is buying government issued securities in the secondary market, suppressing rates and increasing cash in the system. This can also mean increased government issuance. Bond spreads are important. You should look up forwards and the pricing of forwards. They truth about FX is that the rates are fixed. Look up "managed float regime" or "dirty float" if you are interested in that. There are currency pegs, and "soft pegs" going. If you want to study what affects currencies (fundamentals) then you should probably start with a list like this. You could read this book. There are worse introductions to the stuff....
Inflation-adjusted interest rates, volatility, liquidity and their comparison with other country. These are three principle components in the equation of an exchange rate.