Many shifter/derailleur combos don't communicate well with one another; however, 105 and Ultegra share the same articulation/cable pull engineering so you're not just good you're great! I once shifted an Ultegra derailleur/cassette combo with a Dura Ace shifter. Same thing.
I am running a Sugino crank, Ultegra chainring, Deore cassette/shifter/DR on on of my bikes. You have tons of flexibility on which cranks will work. Knock yourself out!