Different features of a wall are good for different types of training. Strength training is done in short bursts of maximum power in several sets. A steep overhang is good for strength training. For this type of training you don't need a long distance, but will need floor space, or area to accommodate a steeper angle. A home bouldering wall is great for power training because you can come and go from your home wall to add additional sets following your recovery.
Endurance training is sub-maximal exertion for longer periods of time.
You can get pretty good endurance training by setting an overlapping 20-move route. Every other day add another hold to the route. A four-panel bouldering wall will make a very good size. This will give you 16' or 5 meters. Interesting shapes will help you keep motivated.