Can't help much with any of the other stuff, but with the maths (as I'm sure you're aware), one of the big SDT phases are the problem solving exercises. One of the biggest handy hints I can remember for this is that the first thing you should do is to work out the distance and speed between all the places on the map by flying / driving / walking etc ... saves trying to do it all while juggling with various options, it's a damn sight easier to just say "Ahh, from A to B it's 20 miles, so that's fifteen minutes" or whatever.
It worked for me, got me through OASC and various other people tried it and had success so I'd give it a go.
And good luck!
-D