BCI: Colombians, Nics, CAs, Hogs +
BCC: "true" redtails such as Surinames and Peruvians. These are the ones with deep red tails.
BCCs do grow larger than BCIs so honestly I would start with a BCI. BCCs are known to be more sensitive to husbandry errors and regurging as well (that I've read). They will also be a lot more expensive than a normal Colombian.
I would get a baby to grow with the species and learn as you go. I wouldn't start out with a huge adult.
And I plan to house my boas in Boaphile/Vision type cages with radient heat panels. IMO adult boas do the best in these kind of setups: glass tanks are okay but I wouldn't recommend them (too hard to keep temps correct). My little ones are kept in tubs.