Switch to AT&T from T-Mobile

Hello and thanks in advance, my question is- I'm going to change to AT&T service from T Mobile service and I want to make sure that all my t-mobile branded phones would work properly on AT&T service.

My phones:
(all network unlocked and t-mobile branded)
LG 90
Iphone 5c
Samsung Note 4

-Would my phones celluar and data networks work on the att network?

-Would my tmobile phones get new updated firmware and software when it's released if used on ATT?

-Would MMS and imessage work?

-Would visual voicemail work?

-Should I just buy ATT branded phones? I don't really want to as I have expensive phones already and would be super expensive to get all new ones.

-Is there anything else I should know before transferring service?

Any suggestions or info is appreciated.