Is this your first time growing apple trees? What is your experience level? Multi-variety apple trees are much harder to keep happy for a beginner. The tree is "self" pollinating because you technically would have three different varieties in one tree.

The description for that tree indicates a full sized (or almost full sized) tree. With the size restrictions you want, you will need a dwarf tree of some sort. So look for someone selling an espaliered tree on dwarfing rootstock. As Paul said, an espaliered tree requires more attention.

And an espalier with three varieties would be even more complicated, unless they were very carefully chosen for similar growth rate.