commons grow up to 18 inches so i hope your planning a bigger tank They haven't been bred small scale in captivity as they dig holes in mud banks to lay their eggs in. It would be a lot easier to breed bristlenose plecs, just add a male and female and lots of tubes and they will get on with it. Mine had 7 lots of fry, they usually have a new batch every 6 weeks or so. theres a thread on here i did somewhere.
if you look at the top of the page on the right, theres a search button. just search breeding bristlenose and there are loads of articles. alternatively google has loads of stuff.
No you won't, they grow 1"+ a month if kept well till they get about 12-15" then slow down. So by the time your 14 like moi, it should be 15" at least really. 24" max. size I think. Would need more than 100g aswel.