I'd say stick with deans if you already have them. They are still a very popular connector. There are other options out there each with it's own pros and cons.

As for your charger, yes you'll need a new charger since that Dynamite doesn't support Lipos. There are lots of good choices for multi-chemistry chargers. Including ones that have built in AC transformers if that's a plus for you.

If you're just getting your feet wet again, nothing wrong with getting a new NIMH if you can find one. In the last couple of years since Lipos have become so prevalent and cheap, the NIMH are getting harder to find.

Once you make the jump to brushless, that would be a logical time to move to lipos.