I want to add to my MP7,1 (16 cores, default video card, 32GB RAM, Pegasus j2i 8TB):
4 x 32 GB RAM modules
1 x RME RayDAT
2 x Sonnet Tempo SSD with extension plate (I want add 2 x 1 TB OWC Mercury Electra SSDs and 2 x Samsung EVO 850 SSDs - for sample libraries)
1 x type A USB card - any recommendation is very much welcome
Q: Are there preferred slots for these cards, or it does not matter which slots do I use for them?
There are physical constraints for your cards width wise. That puts some constraints on where they should likely go. ( a bit of a waste to put a single width card into a double wide slot).
Apple's support document.
Learn about the PCIe slots on your Mac Pro (2019) and how to install additional cards.
support.apple.com
The RME card is pragmatically a double wide card. So you will need one of the double wide slots in the MPX bays that are open. ( slots 5-8 won't work as they are all single wide. ). if have the MPX 580X video module, then slot 2 is a reasonable place to put this.
The Tempo SSD cards are PCI-e v2 x4 , so any single width x8 slot would do ( actually a bit of overkill).
[ if these are previously purchased (already owned) and/or used then makes sense for an invested, "sunk cost' sense. If looking for something new Sonnet has a newer card now for 2.5" drives.
https://www.sonnettech.com/product/fusion-dual-ssd-raid/overview.html ] .
Type A USB card with how many ports, how much power , and how independent the sockets? ( cards can come with 1 , 2 , or 4 USB controllers for a variety of sockets. ). These will highly likely be single width, so again no sense in "wasting" a double width slot on one of these. A card that is purely PCI-e bus powered will simplify things ( don't have to buy more power cables). Again unlikely to go past x4 PCI-e lanes ( and often PCI-e v2 so again 'overkill' in terms of bandwidth of Mac Pro 2019 slots; any of them. ).
If the Mac Pro PCIe "Expansion slot utility" manager app seems to suggestion a "problem" of oversubscription there isn't. That app is more so "slot occupied." and "Thunderbolt port being used" than a dynamic measure of oversubscription. A suggested potential problem more so than one with these kinds of cards which have relatively low bandwidth requirements. You are not going to creating any "chokepoint" with any of the above cards at all. You could randomly insert them into the MP 2019 where they could possibly fit and it wouldn't make much difference at all.
One configuration with an eye to future replacement/ expansion would be:
slot 5 : tempo card (eventually replace with multiple M.2 drive x16 PCI-e v3 card )
slot 6 : tempo card ( eye toward eventual x4-x8 PCI-e v3 storage card )
slot 7 : USB card (presuming it doesn't need extra power cable.)
slot 2 : RME card ( double wide)