LiPo - things to consider?

[patchfoo]

I am very new to R/C cars. I have a 4WD 1/10th buggy - Tamiya Durga DB01. I built it completely with stock standard (basic) parts which I am now hoping to upgrade. I am looking for an upgrade to get more speed/acceleration and the way I see it I have two options:
1. Upgrade the motor (brushless I assume)
2. Upgrade to a LiPo pack

What approx speed upgrades would I get for each?

I like the idea of upgrade to LiPo packs because I want to get a secondary battery anyway.

What things are there to consider when doing this upgrade? I know I will need to get a new charger because mine is only for NiCd and NiMH. Is that all I will need? I think I read somewhere that you need a better ESC or some other electronic part when switching to LiPo. Also, my buggy has space for traditional 6 cell packs but LiPo doesn't come that way. Is there a specific type of LiPo I will need?

Any help is much appreciated! Thanks!