I'd go with two.
Mine started out with one Talon Khorus sub. Then I built 2 sealed and 2 ported cabs all using the same 10" Morel drivers and powered by 2 Dayton amps. Awesome results and I was initially going to sell the Talon. Until for kicks decided to put it back in. Hate to diss a pioneer like Geddes but the improvement from adding that 5th sub was pretty big. Especially in terms of apparent extension. For whatever reason I do not understand the same sub that never did make really deep bass when used all by itself suddenly now when added to the other 3 makes awesome subterranean bass. So now my DBA is five and I say when it comes to subs more is better.
I'm all about thinking and being creative in getting the most for the money. Even though I have two Dayton amps the main benefit of two was being able to try different things and learn that connecting for 16 ohms sounds a lot better than 4 or 8. There's four times the power and 6 dB more volume at 4 vs 16 so it doesn't seem like that would be the case. What happens though is the extra power and volume only makes a difference on the brief few peaks where you would otherwise be clipping, while all the rest of the time it gives bass that is not nearly as taut and tuneful and well controlled as at 16. Whereas with 16 it sounds better all the time, you just have to be careful not to over drive it because these Dayton amps sound just awful when they clip.
So since you are hands-on capable I would suggest looking at your amps and speakers and considering wiring them in whatever combination will get you to higher impedance with fewer amps. In other words run them all off one plate amp, or two, whatever works with what you have. Because I just don't think you will get much if any benefit from buying more amps.
The other nice thing about having four vs three is it seems to me from everything I've read and done that the more you have the less it matters where they go. I mean technically yes of course it is hard to see how it would not matter. With one sub it certainly does. With four or five though I have moved them around one or two at a time and not noticed any difference. Maybe with the right music? Dunno. Tim I'm sure will chime in. He has even more experience than me, except when it comes to DIY.
Mine started out with one Talon Khorus sub. Then I built 2 sealed and 2 ported cabs all using the same 10" Morel drivers and powered by 2 Dayton amps. Awesome results and I was initially going to sell the Talon. Until for kicks decided to put it back in. Hate to diss a pioneer like Geddes but the improvement from adding that 5th sub was pretty big. Especially in terms of apparent extension. For whatever reason I do not understand the same sub that never did make really deep bass when used all by itself suddenly now when added to the other 3 makes awesome subterranean bass. So now my DBA is five and I say when it comes to subs more is better.
I'm all about thinking and being creative in getting the most for the money. Even though I have two Dayton amps the main benefit of two was being able to try different things and learn that connecting for 16 ohms sounds a lot better than 4 or 8. There's four times the power and 6 dB more volume at 4 vs 16 so it doesn't seem like that would be the case. What happens though is the extra power and volume only makes a difference on the brief few peaks where you would otherwise be clipping, while all the rest of the time it gives bass that is not nearly as taut and tuneful and well controlled as at 16. Whereas with 16 it sounds better all the time, you just have to be careful not to over drive it because these Dayton amps sound just awful when they clip.
So since you are hands-on capable I would suggest looking at your amps and speakers and considering wiring them in whatever combination will get you to higher impedance with fewer amps. In other words run them all off one plate amp, or two, whatever works with what you have. Because I just don't think you will get much if any benefit from buying more amps.
The other nice thing about having four vs three is it seems to me from everything I've read and done that the more you have the less it matters where they go. I mean technically yes of course it is hard to see how it would not matter. With one sub it certainly does. With four or five though I have moved them around one or two at a time and not noticed any difference. Maybe with the right music? Dunno. Tim I'm sure will chime in. He has even more experience than me, except when it comes to DIY.