The module system is a great system, which I used in the Ultimate and now in the custom 45. It has worked flawless for me with many rounds sent using both rifles.
I would suggest..... its correct to think hard and long over what you may eventually end up with but, don't over think it.
You've mentioned the type of hunting you normally do and a Knight UL and BH would work just fine for you. But, if your intentions for future use is to also use SML, then a custom or semi-custom, such as an Encore or CVA conversion would work fine for your style of hunting. Just remember, in MI you can use a SML during the general season, but not in the dedicated muzzleloader season. I also do not believe a SML will be legal in MI.