Have a choice to consider flying either TAP or IB for a round trip (MAD-LIS). TAP tickets are slightly cheaper for date and time of my plan. Never flew TAP before. Here are my questions:

1. For a short flight like this, simply go with price?
2. Should I be concerned about IB’s existence in 3 to 4 months?
3. On TAP’s web site, can’t find way to add UA FF number (want to get UA miles) to reservation. Just call?

Thanks in advance.

Moderator, I am aware that this post can be on *A or 1W (or both). Do what you think is appropriate. Thx