1. Driving on kerbs damages the tyres, you should avoid it. You can check the wear rates in engine.ini:
As you can see, driving on rumble makes your tyres wear about 8x faster.
tyreweartarmac = 0.0006
tyrewearrumble = 0.0050
tyreweargrass = 0.0400
2. You should drive as fast as you can without going off track . Retaining speed in corners is good, and for this you need to be on the outside before turning, thus making the turn softer. Sharp corners are the only place where it is justified to drive on kerbs. In long, soft corners, try driving on the track. Also, hitting other cars damages your tyres! Avoid contact with other cars. I usually keep in mind that I want to get OUT of the corner as fast as possible, in contrary to getting as fast as possible IN the corner. So I take my time, position myself, brake, and then when I'm ready, I apply throttle. Generally, brake and throttle should only be applied once in a corner.
3. I sadly did not notice the effect of braking+turning. Maybe it's because you only do it for a split second.
4. If the car brakes effectively, then it's no problem, but I guess your fuel consumption may be a tiny bit higher.
5. KERS makes you go 1-2 seconds faster on ANY track. Sadly we didn't address this issue when asking Simon for update.
You should be able to easily do either a 5H + 5H or 4H+4H+2S strategy on pretty much every track. I would advise to set the lapcount a bit higher (around 15 laps maybe?), which would make the soft tyres a tempting solution. In online championship most races are over 20 laps, and we usually utilize soft tyres.