Vquestor, your approach to Firewire is good if you are thinking of using a LT some day.
In general, my preference is to use one host and load the soft synths and effects you need. It is clean, elegant and reliable. There is also less potential for conflict when you use only one soundcard.
I was just thinking if you ever wanted to use Kontakt and the B4 as a standalone together it would be easier with two soundcards. This allows you to use all the manuals and bass pedals of the B4 layered with other sounds from Kontakt. You can do the same thing in a single host but you have to bring up more instances of the B4. In any event, I agree with you 1 host & 1 sound card!!!