Obviously a keeper doesn't need to be as aerobically fit as a midfielder, but it doesn't hurt. Look at the bip test as a challenge. Don't worry so much about running to get to a level, as much as giving everything you can on the test and improving from there. Flexibility shouldn't be a major issue. If your weight is back, you probably need more speed in setting up your slide and need to keep your top shoulder and hip forward as you execute the slide.
Flexibility is still a good thing to work on.
I was wondering what sort of paint I could use to colour them, some paint that wouldn't rub off on sand turf but also wouldn't come off when it got wet, and some that wouldn't destroy the kickers. The recent modification to FIH rules was written specifically for internationally televised tournaments like the Olympics or World Cup. They do not apply to most local leagues unless your association has a specific rule, but all you have to do is ask. Use an enamel paint, preferably spray. Be prepared to paint frequently and heavily.