Earlier tonight I looked at some other commercial/shareware software sites to see what others did...and yes, I think you'd be better with completely defining what a single license allows or not...
As I wrote before, I think a single license should allow for a person who has (or access via flash to) more than one PC but who doesn't have other people that could use the appl simultaneously...but require a second license for other PC(s) if it can be run by another person(s) at same time.
Regarding multi-copy discounts: It seems that having a small discount for copies 2-3, 2-4 or 2-5 is somewhat common...with percentage around 10-15%...then maybe a second tier from that nbr to 9 copies; next tier from 10-19 or 10-24; next tier at 20-49 or 25-49; and last tier at 50+...because I'm presuming you'd very rarely get more than 50! You could always have a "special volume pricing may be available on request" type note...
Also, having some sort of an educational pricing that is a bit different seems typical...and as I wrote, maybe a very slightly different (lower?) price for small numbers (less than 5) of copies for home use than for business...like 10% off for business and 15% off for home?
BTW, on web page for this, you have as benefit: "free support via online forum"...but usage of forum is open to all, and I don't think making it restricted would help any...it would discourage folks who are trying it out, I believe...and some of us are trying to help out with answering queries to reduce the load on our dedicated author!