Beginner Gardening: Vitex agnus-castus var. latifolia .. Need to know about this, 2 by RESORT2ME

RESORT2ME wrote:
The base is split at the ground into two 6" trunks. One appears to have been pruned close to the ground. The other was cut off about 6' tall.
We moved here in May 2012. I thought the whole thing was a dead trunk that I'd have to dig it up to get rid of.
Next thing, I see shoots coming out everywhere. It bloomed surprisedly grand.

!. I now read where these trees grow to be quite large. It is 15' from the rear of our house. If I'm to move it, will these trees take that well?

2. Since it sprouted and bloomed so well, shall I cut back all growth as it was, or can I prune leaving limbs that will sprout more, giving more blooms?

3. If I wish the tree to grow a bit taller, do I leave only one shoot up-top, or 3 or 4?

4. What kind of root system do these have? The tree is now located 20 feet from the closest septic drain line.

If I can't move it, I'll prune it bare each year, so it doesn't touch the house.