So what are your concerns about the breeder? I've read this whole post and still don't understand.
If its because he's offering you a free Normal with a purchase of a Pastel, that's because Normals don't go for a lot of money nowadays so breeders will often give them away so they don't have to feed an extra snake.
In regards to cohabitation, did he actually suggest keeping two snakes together or did he just offer you two snakes? It's really up to you to do the research into the husbandry and care of the animal. Cohabitation is not recommended to newer keepers. It can be done if done properly (I speak from personal experience). It's a highly debated subject, but by no means it's wrong to do it.
I think if you don't have the funds right now, I'd wait on the purchase of the snake. First, buy all the necessary caging equipment for the animal and make sure the husbandry is correct and then purchase a BP. The proper setup starting costs could be pricey (caging, thermostat, hides, thermometer, etc.).