As someone who started out as a novice with a similarly small space to work with, I went with the Belgian fence approach and I think it can work really well.
For reference, the first Belgian fence I set up runs 48 feet east to west. There are twenty-five trees planted two feet apart. I think all of them are on G41. I used eight foot black locust splits for the end posts and green garden t-posts for the intermediate supports, set eight feet apart. I made the trellis by tying bamboo to the support wires (my dad grows bamboo so I was able to get that for free), and I train the trees to the trellis with green velcro garden tape. I have to fiddle with it now and then, but it’s worked out pretty well so far (probably better than I had any right to expect).
The fence has not completely filled in yet, and we’re just starting to get fruit (started with bench grafts so it was going to take a little longer). But I’m happy with the way things are going so far, and it looks like most of the trees are ultimately going to be fine in terms of filling in the space.
Pros of the Belgian fence from my experience:
It takes up minimal space in a small yard.
It makes it comparatively straightforward to manage a lot of varieties in a small space. (Compared with a multi graft tree.)
As a novice, I haven’t found it especially difficult to train the trees. While there was definitely a learning curve, training the trees was much more straightforward than it would have been with more demanding forms of espalier or with free-standing trees.
Also speaking as a novice, I feel like it’s made it easier to take care of the trees overall.
It looks cool.
Cons:
It involves a certain amount of fiddling and fussing, what with multiple rounds of summer pruning and tying the trees to the trellis and straightening the trellis when it gets a little out of whack, and of course setting the trellis up in the first place. (I enjoy working on it, actually, but I can understand why some people wouldn’t.)
More trees = more start-up cost. (I mitigated this significantly by buying rootstock and grafting my own. The materials for the trellis itself were not especially expensive.)
Dudeness suggests that espalier pruning reduces overall production. That may be the case, but I’m not sure. (Tall spindle systems and the like are supposed to increase production compared to traditional free-standing trees. Espalier offers some of the same benefits, and the Belgian fence is particularly advantageous form of espalier in terms of maximizing scaffold length in a given space. (Thank you, Pythagorean theorem.)
But honestly, I don’t know how the productivity of a Belgian fence compares with that of freestanding trees, and I’m guessing it might depend a lot on your particular situation.