I guess maybe I didn't ask the question right. This is the first time I am building up a bike and don't know the appropriate jargon yet. I am looking to find a setup that makes the chain tight enough not to fall off the crank or cog when I jump off a curb or something. I don't care about the actual chainlength- just the ability for it to stay on. So I'm assuming what I want is to know the number of chainlinks/halflinks with what sized cog to work with the Omnium chainring at a gain ratio of somewhere between 5 & 5.5

Why should I use an indecent crankset? From the limited searching I did, The Omnium is one of the cheapest 144 BCD Track cranks I can find that I like. If there is one cheaper and better let me know and I will look at it. I'm using a cassette hub with a cog and spacers because I thought it would be a cheap easy way to deal with chainline issues of putting a track crank on an old 1990's MTB frame. Is there a SS MTB hub I could swap that would be compatible with the Omnium chainline. I was under the impression that SS hubs didn't give you as much lateral flexibility in regards to the placement of the cog. This is why I was looking for a chart or something that would show me what kind of hubs work with what kind of chainrings etc. As i'm doing this I realize the more I learn the less I know. Appreciate any suggestions.