I need a card to cover minor expenses during business travel when AMEX is not accepted (my employer wants me to use the corp AMEX card first).

Prior to posting this I *did* search the boards quite a bit and did not find threads that seemed to match my specific scenario -- the ones I found were brand newbies...

parameters:

--I will hit UA PGold (is that P1 or P2?) first week in December on segs, currently only 35,869 miles.
--I earn status on segs, and figured out next year, under current trends, by adding one seg each trip I can hit 1K.
--My annual travel is not enough to spread among other liners...so pretty loyal to United in order to max my status -- mid-level traveler.
--Heaviest travel tends to be Q1 with a steady flow the rest of the year.
--Almost all travel regional NE. Usually UA with a smattering of US due to schedule/price.
--Purchases with this card will be minimal -- as described, to cover meals/work purchases when AMEX is not accepted.
--I've never done a club/lounge -- usually no time to mess with it...and when I do have extra time I just hang at the pub for maybe an hour max...Am I really missing anything for my style of travel?
--I guess my ultimate goal is to max points since I earn status on segs, but open to a new way of thinking about this.

Questions (I have answers in mind but want to see what others say to confirm or refute my suppositions):

1--Will I be better served by the UA or US specific cards, or should I be looking at the 'non'captive' cards (Citi, Chase, etc).
2 -- Visa or MC more widely accepted?
3 -- The cards I have seen have a purchase requirement to get the big initial bang...am I missing any that drop a nice chunk just for opening?
4 -- (related to #3): Seems to me if the initial points add is still short of the 75k for PPLat, then should I do this just after first of year?
5--What impact, if any, can I have on the *A program? (or am I pretty much where I'm going to be already?)

Long post, thanks for bearing with me.