Lighting Questions For New 20L

'm planning on setting up my first reef. Its kind of out of the range
of the nano designation, but I figured you guys would still be the
best referece, becuase it is still a small tank.

The setup was going to be like this. I was building a big wood
cabinet, and was going to use a 20L as the display tank, built into
the cabinet. A 10g was going to be mounted above it, hidden (will look
like drawers on cabinet) and used as a refugium. Below the display was
going to be a second 10g for use as a sump.

1. Do I really need the second 10g as a sump? Is it worth it?

2. I saw $35.99 150w HQI MH bulbs onsale at petliquidators.com or
something like that. Would a single one of these be ok for the 20L, or
would I be better off with two 70w bulbs. I'm worried about the single
bulb not having a wide enough range. If I was thinking about using
this as my only bulb, should I go with the 20K, or 10K bulb? If not
only bulb, what sort of suplements? (on a budget)

3. What could I grow coral wise with the 150 watt bulb? How about with
150W bulb (say 10K) and NO fluoros for actinic, say 2x 15w.

Also, are their any cheaper ballasts for MH lights. I could swing 2
70 W bulbs without too much of an issue, but if its gonna be $35 for a
150 w with a $60 ballast, or 2x $25 (bulbs) and 2x$50 (ballasts) for
the 2 70w setup...you can see where theres kind of a big price
difference. Could I run two 70W bulbs off of one 150w ballast? Maybe
do some math, some good old Node-Voltage or Mesh Current equations and
put a resistor in parrallel with the two bulbs and give them 70W each.

I would love elect. ballasts, but I can't afford to sling 2 $130
ballasts over this thing.

The 150 W bulb is available in 10K, and 20K. (at the $35
The 70w bulbs only seem to be available in 10K. (at the $25 price)

Thats all the questions I can remember for now. I'm sure I'll have
more.
Feel free to flame if I deserve it