Yes you can get ignitors seperately, but they are pricey. Check out Wal-mart for engines. The Wal-mart Estes engines come with extra plugs and ignitors and are way cheaper than mist hobby stores.
should be fine since most kits are carboard tubes. I am guessing you will not get much height due to weight. Be careful as it will be lethal coming down. Start out with samll engines and work your way up.
We had a parachute fail on a fairly heavy carboard kit one this summer and it was a missle coming down that buried 8" into hard ground. 8)