2. focus on the business, not the software (freshbooks!). This also means that if you need more than your 15K, start hunting for financing or cash _now_. Cash flow > everything else. When you're sweating laundry money and forgoing Starbucks or a pint at the local NOTHING gets done. You just have to punch past the line where you're "adding features" and instead "fulfilling business needs". A business that's bleeding red has more value than a finished product w/o customers and their attendant baggage - sales marketing support etc.
3. show off the product to many before you think it's "ready", because otherwise your baby will never be ready. Don't even think about competition until you have something competitive - and if you're in internet business, the market is big enough for everybody. Never lie, but do promote your shit to anyone who will listen.
4. Set up a proper dev and DVCS from day -1. Write functional tests so you can at least know if you break functionality while adding features. And docs rule. (Almost) always write code like you won't read it until 3 months later.
5. outsource and manage-host _everything_ reasonable
6. If it's consumer facing software and not middleware - UI IS EVERYTHING. And UI always takes way longer than the so called "hard stuff".
7. always push yourself: not to the limit, but just beyond where you think you can go. The "I can't believe I did that" feeling is my personal favorite.
And there will be a lot of feelings. This rollercoaster ride will be rough, but when you're on the way up or at the top ... BOOM ... spring in your step ... pebbles in your shoes ... Michael Phelps ain't got nothing on me (ok, that was extreme, but the "I AM KOBE" effect does rock).
In case you didn't read it, Young Money intervied Mark Cuban recently. He says it all better than me: http://www.youngmoney.com/entrepreneur/entrepreneur_profiles...
All the best!!!