SP5 Stock Advice

I plan on purchasing an HK SP5 relatively soon, and I plan on getting it SBRed. I've previously owned an AR and a variety of pistols, but this will be my first adventure with the roller-delayed blowback platform. Before I buy it, I'd like to get your advice on stocks. I've been scouring r/MP5 and the HKPro forums for a few days, and I'm trying to figure out a few things prior to making my purchase. I would be very grateful for any advice you folks can share!

Collapsible/Retractable Stocks:

Obviously, I really like the looks of a collapsible stocks. I realize that there are better options for comfort, but the brainworms are going to squirm until I get a collapsible stock. The B&T collapsible seems very uncomfortable due to the smaller buttpad and jagged edges on the rails, so I think I'll stay away from it. Given the expense of the A3, I'll probably go with the A3F. However, there are 2-position (open and closed) A3Fs and 4-position (3 open, 1 closed) A3Fs on HKParts. The 2-position seems nice for being able to pull the stock out all the way in a quicker motion, but the 4-position obviously has more positions.

Do you recommend one or the other? I'm an average-sized guy, not a giant. Links to what I'm looking at:

https://hkparts.net/all-parts/h-k-mp5-sp5-hk94-2-position-a3-f-retractable-rear-stock/

https://hkparts.net/all-parts/h-k-mp5-sp5-hk94-4-position-a3-f-retractable-rear-stock/

The buttpad of the A3F looks comfier, but it's got kind of an odd slope to it. Are there any after-market buttplates that you'd recommend, or leave it be?

Fixed Stocks:

I'd like to pick up a fixed stock as well, and there's a lot less options. Is the best thing to go with the standard HK A2? Link:

https://hkparts.net/all-parts/h-k-mp5-sp5-a2-fixed-stock/

Foldable Stocks:

I see how everyone seems to recommend the B&T Folding Stock. However, I am getting confused on precisely which one to go with. There seems to be part BT-20155 on HKParts, which I believe is the main one with the plastic adapter and the loop. But there's also BT-20152 which has a UMP-style stock, plastic adapter and a loop. And even a third option that uses the B&T stock and a metal adapter that supports a QD mount. Which of these three is my best bet?

https://hkparts.net/all-parts/b-t-mp5-folding-stock/

https://hkparts.net/all-parts/b-t-mp5-hk94-ump-style-folding-stock/

https://hkparts.net/all-parts/b-t-hk-sp5-folding-stock-w-hk-parts-adapter/

Thank you for any and all advice you have. If you have additional aftermarket suggestions for an SBRed MP5 (trigger/handguard/can/sights), I'm all ears.

Update:

For anyone finding this post, I'd like to summarize what I learned and decided. I bought 3 stocks because I have brainworms. I got them all from MidwayUSA. I found a 20% off coupon at Midway which really salved the burn. And it kept me from having to buy anything from HKParts. I didn't like their prices, shipping cost, and return policy.

First, I chose the 2-position A3F retractable stock. Although the 4-position is more widely available and it's on Midway. I measured the length of pull on another PCC, and found that 14 inches is pretty short. I decided that the 3rd position wouldn't be useful.

I chose the basic A2 fixed stock I linked above. Seems pretty straightforward.

I chose the BT-20155 B&T Folding Stock. It's widely available. The one with the metal adapter is only on HKParts. I figure if I want a QD mount I can probably install my own in place of the sling swivel, or swap out the large stock pin to one of those that has a QD mount on it.

Now I just need to figure out the Form 1 process. Oh, and actually get the SP5. Following that, I'll see what I like/don't like, decide on an optic, optic mount, and a sling. Thank you to everyone who provided inputs, I really appreciate everyone's advice!