Rit - I'm not an expert on apples and crabs, but I ask questions of experts at Penn State, Purdue, Mich. State, Cornell, and guys like Maya and Appleman on this forum. ( Maya and Appleman are orchard owners. )
What's the soil like where you intend to plant - sandy or clayish-loam ?? Guys that have sandier soil on here say B-118 rootstock is a good choice for that soil type. For heavier, clayish-loamy soil, the recommended rootstock is MM-111. I got that info from the head of Penn State's fruit tree program. Those rootstocks - ( B-118 & MM-111 ) will grow trees to around 18 to 24 ft. tall, and first fruit in 4 or 5 years. Those tree sizes are typical for most wildlife planting guys. I hope this helps and doesn't add to confusion.