You more or less answered your own question. When it comes to hash power it doesn't matter at all whether you have divide your cards to more rigs.
It's usually easier to set up a 4 gpu rig, less issues, they somehow solve themselves, cheaper power supplies and a better choice. The downside is more CPUs, motherboards, RAMs, hard drives etc. - it can add up! On the other side, testing anything on a 13 gpu is expensive, anything goes wrong with a 13 gpu rig - you lose a lot of money. If I would start all over now, I would get 8 gpu motherboards. It seems to be a good number where you still have enough gpus there to save money on hardware, you still can get a decent power supply solution and you still don't get to many other issues.
As of power supply, I use all kinds: regular, "mining" and server. I've managed to make everything work. If I would start over, I'd get only server supplies for gpus with some regular pu for the motherboard, cpu and hard drive. Mining ones are a new thing, my guess is they are not properly tested and just an extension of the regular pus. Server ones are cheaper, quieter, have all kinds of protections in them, and best of all, they are built for 24/7 operations by serious companies.
I don't think there is any difference worth worrying about the add2psu and other solutions. I've used all of them, now I prefer anything with less electronics, I just find something to connect the pins (properly!).
Thank you for your answer. And thanks for advice about using server power supply. So I should leave everything as is, splitted 4 cards per rig if there are no effect to finding shares
Now I have:
3x ASROCK H81 PRO BTC R2.0 with 6 slots (4 gpu each)
1x ASRock H110 PRO BTC+ with 13 slots (7 gpu)
1x Biostar TB250 BTC PRO ver 6.0 with 12 slots (4 gpu)
I bought everything while there were in stock. And I was planning to buy more GPU, but those are now double priced.
I bought RX570 8GB Sapphire NITRO+ DUAL for 246 euros per piece, now they are 449 euros per piece. For RX580 8GB Sapphire PULSE DUAL 279 euros now they are 499 euros. For RX580 4GB Sapphire NITRO+ DUAL I paid 222 euros now they are 449 euros
) and prices are VAT excluded... Crazy prices now..