Good day. I have a newbie Single speed conversion question that maybe some of you grizzled vets can help me out with.

I am converting an old geared MTB to a SS townie bike and have basically stripped it down to the frame and am building it up. I am getting a new drive train and have decided to use an omnium track crank with a cassette freehub and try and take care of chain tension with adjusting cog/size half links because I really don't want a derailler style Chain tensioner and don't want to spend the dough on building up a wheelset with an ENO hub.
But I want to know if there is a way to calculate the chain tension based on the size of the chainring and cassette choice, distance between BB & rear axle, chainsize etc. before I plop down the cash to buy everything and experiment. I have read other people say that you have to experiment to find out if it will work, but I certainly don't want to buy a crankset only to find the chainring is incompatible or buy half a dozen cogs to find the right fit that works around a desired gain ratio. I don't know if this makes any sense but is there some online chain-tensioning calculator somewhere that I can plug variables into and it will tell me whether it will work? Or at least some mathmatical formula or rules of thumb?

Thanks for being patient with my silly request.
-g