As other have said allow 2 hours. Outbound immigration can be slow at times and it can often get slowed down as people try to queue jump and the officers have arguments with them.

BA Lounge is very run of the mill, standard priority pass fare.

I used to do the IST run very regularly and I started with BA and I very quickly moved to TK, much more convenient and they have the airport all sown up.

Last time I went, the electronic device checks at the gate was a total mess but I think they've got better at it.

E-Visa all the way. The queues at immigration very much depending on what time you land but at the best of times their is always a wait. If you get a fast track voucher you will often find yourself the only one or 1/2 in front of you.

Enjoy, Istanbul is one of my favourite cities. up until April of 2017 I've been going regularly since 2005 so it's a bit of a second home. When I first went which IIRC was in 2002 all the cars were the locally made Fiats. Whilst you still see them the amount of VW and other germans marques driving around has quadrupled.

Unfortunately for your trip this time all the best Kebab places are all in the suburbs and the best one is on the Asian side.