Nice job, 17. Sounds like you took the "sage" advice of "thyme" honored chef's.
I think starting with ale would dictate the rest. If you want the yeasty- tangy-carmelly body of the ale to remain as a flavor, (which I would in this case), I think your lemon and mustard were perfect complements. Then some sweetener and you should have a winner.
I always recommend tasting, tasting, tasting as you go when you are inventing. I usually use more nose than taste sometimes. I'll smell my beginning ingredients and smell the items I might add as I go along.
If you use ale, molasses and chili pepper, this could be the cornertstone of a very useful marinade or cooking sauce.
I also swear by ziplocks for marinade.
I learned something from an info-mercial. If you can remove the air from the bag (as in a vacuum bag) the marinade is infused into the flesh of the protein even faster and deeper. I squeeze all possible air out of my ziplocks and have even resorted to putting in a straw and sucking out as much air as I could "manually". This is especially effective for quick marinade as in 20 minutes before cooking.
So, when are you making this steak again?