Here's some answers to your questions - all of which I've asked myself in the past:
1. Definitely fly through Gibralter as its only 40 minutes max from Tarifa, where as Malaga can be 2 hours if the traffic is bad. BUT if you are hiring a car look online for hire companies that are based in Spain, just outside outside the Gib border - driving in and out of Gibraltar can take forever as there is always a traffic queue a mile or two long. The airport is literately 5 minutes walk from the border.
2. Waves depend on a couple of things, mainly whether its Poniente wind (cross onshore from the right, across the whole bay) or Levante which is offshore from the left, in town but cross shore at the far end of the bay. Its been blowing Levante for over 20 days straight now and we've had little or no waves at all. The one Poniente day had some small waves but really only 1 foot or so on the inside, if you do get this she can body drag out pass them and then its all good. Alternatively there is a lagoon, which is dead flat and ideal but it can get busy if it is the right conditions but due to the nature of the Spanish culture just get down the beach early and the beaches are generally alot quieter, especially on the weekends when everyone is up drinking until the early morning!
3. Poiente - just look for the beach where there is space - probably further away from town up towards the dunes as the wind will be more cross shore, which always helps beginners! Levante always just head to the far set of beaches - the furthest beach is probably best for beginners as its wider and the wind a little cleaner, but the Spin out center or Valdevaqueros are great places to chill and watch the action (ie, when your girlfriend gets tired and wants to sit and sunbathe whilst you carry on riding!).
4. It can be, but more so at high season. Just ensure if you leave stuff in the car its not visible and in a closed boot. Weekends are busy but there are loads of parking attendants now so that helps. Hasn't been a problem since we've been here the last few weeks.
5. Not sure about that really, the old town has alot of restaurants and after 11/12, its where everyone goes to drink and party, generally in the streets until about 3 then on to the clubs. There are a few places on the front down towards the football stadium - Sushi at Surla is amazing (and the breakfasts and lunches are pretty awesome too).
6. Probably windier more than 60% but you will get days when its probably too windy to kite in tarifa so you either do something else or look for other lighter wind sports (Canos de Maca, Los Palmones or Getares) - for non wind activities, visiting Vejer de la Frontera (the White City) is worthwhile - old town out on a hit top, nice to wander round and good tapas! We did a day trip to Tangers this week and its was excellent, take the ferry from Tarifa port (www.frs.es
), if you go drop me a message and I can recommend a really great guide - we were just gonna wing it ourselves but we would of got lost and wasted so much time, instead Morit was amazing and showed us some much amazing stuff. I haven't been to Gibraltar for several years but my memories are of it been pretty naff, but if you're desperate for something to do could be worthwhile. Hiring SUPs is pretty popular lightwind activity. Unfortunately I'm not great on the no wind activities, I leave that to the wife
Hope that helps
We're heading back home on the 2nd June, but you'll have a great time, this is my 7th time in Tarifa and it never disappoints!