buy the mics you know you'll want down the line immediately. In any audio chain, the transducer is the strongest link. Does the mixpad provide phantom? If it does that makes it much easier to upgrade your mics. Buy some great mics, and run those through the mixpad for a while. Or, you could ditch the mixpad, buy a PS-2, and line txformers and run straight into the D8. Does Doug Oade still modify the frontend on the sony decks? That might also be something to look into. After you get some more cash you can buy a "real" pre and later an A/D. If you like the 300's, you should seriously check out some 480's.
I've found that the AKG's sound best (to my ears) through some sort of transformer pre such as the Soundevices boxes or the EAA/AETA ones. They kick mucho ass in front of a m148, but that's highroller territory. I've also heard good things from bean and others about the DMIC.
As for A/D, for me apogee's the name of the game. I've had my 500e for 6 months now and I'm not thinking about retiring it any time soon.
Bottom line: Upgrade your mics first the way you want to and the rest will fall into place.
Welcome to gearsluts anonymous. Can I be your sponsor?
+T!