Unique id - sequential order (and linking between forms)

I have two questions:

  1. Is there a way to generate a unique id that consists of a sequential number? (eg. 001, 002, 003).
  2. Is there a way to use this id to link submissions between two different forms ?

Here’s the scenario:
Let’s say there are 2 forms.

On the first one, I’m registering Users that will benefit from Services. For each submission I would like to automatically generate a sequential code (001, 002, 003). If this isn’t possible, it’s ok, I can manage with non-sequential, as explained here.

Then, on the second form, when registering Services that have been provided, I would like to say who benefitted from it. Is there a way to pick from a list of existing Users?

@ivanradisson, maybe this approach discussed previously should also be helpful for you: