If I were first starting out with boas, I would go with an albino or a salmon. Salmons are normally around $100 and albinos $250. Males do stay quite a bit smaller than females, but both will grow depending on how you feed them. Males are normally around 5.5 - 6 feet and females around 7 - 8 feet. Females are much thicker, however. It is really up to you to determine which size you want. I personally like the females better, because of their size.
It is possible that your boa could have IBD, just as it is possible with pythons. However, pythons die much more quickly than boas. Buy from a reputable breeder to be on the safe side. It may also be a good idea to buy from a breeder who breeds both pythons and boas. If their boas had IBD, their pythons would have died.