Quantity of subs don't matter too much, whether 2, 3, or 4. What matters is the response at listening position. The more subs you add, the flatter your response can be, and the less need of equalization. Geddes has his approach, Harman has theirs, and there have been others, but the goal is mostly the same.
As for near-field, some people really enjoy that effect, others do not care for it. I say give it a try to see how you like it. There have been theories bandied about that near-field can feel a lot more powerful even for the same SPL, but I haven't seen any scientific substantiation of that, merely some educated guessing. I am not saying that isn't true. I don't know for sure.
Regarding mismatched subs, it doesn't matter very much so long as you never reach any of the individual sub's limits too soon. A problem with wildly mismatched subs is a weak subs can reach its limit much sooner than a powerful sub at which point it starts generating a lot of distortion and degrades the sound overall much more than if the system had not included the weak sub at all. If all your subs have roughly the same performance characteristics, that won't be a concern.