Marc,
The beachtek adapter is not needed with model MKE300 sennheiser
mic which already has a 1/8" connector.
If the mic you choose has a 3-pronged connector you do need the
beachtek adapter. It is a good device and I have used it a lot
with a Sony TRV900 camcorder. It also allows you to take a line
feed from pa and sound systems.
You would need a cable to go from the mic to the beechtek. A
short cable for ease of use.
A long cable for remote location from camera, if you need to tape
a panel discussion or pass mic around.
You have to be concerned about mic noise of course. Connections
and handling introduce noise. Headphones?
Try to review your footage as you go, learn from your mistakes.
don't zoom with impunity. do change shot setup or angle, rather
than stay in an poor one.
But don't wear out your tapes with viewing. Dump onto hard drives
or make vhs viewing dubs?
Hard drives are going to be an investment.
Start thinking about editing now.
B&H sells generic batteries too.
http://www.beachtek.com/dxa4.html to download info and
instructions if you need them.
THere are some good books out there,
Directing the Documentary, by Michael Rabiger, seems popular.