First, ((hugs)) mama! I imagine that there is heightened anxiety anytime a child has something like this. I know that my stress level was through the roof when I delivered pre-term twins via emergency c-section and they were in the NICU (and I had two more at home, too), so I can kind of relate. I hope you are taking care of yourself, and getting some rest and help with that two-week old plus older kids.
Second, I agree with much of what others have said. You did the right thing by leaving your new son intact. No sense exposing ANY child to an open wound in a diaper and risk of bleeding, and in particular one who has a known "issue," however insignificant that issue may be in the long run.
No retraction needs to happen, ever.
If your son is making urine and is growing and developing normally, why would any further follow-up of any kind be needed? Is there some long-term risk or procedure that requires you to establish a relationship with a urologist NOW? I sometimes think that we seek specialist care (this definitely includes me, so this is NOT critical in any way!), and of course specialists are trained to find and treat problems ... not to tell you that everything is fine.
If I were you, I would seriously reconsider the need to see a urologist, and I would also find a different pediatrician who is more knowledgable about the foreskin. It may not be easy. You might even consider a family practitioner or a nurse practitioner, depending on what's available where you live.
In the (UNLIKELY) event that your son does require a urinalysis, try to use a sterile bag. If cath is required, I would VEHEMENTLY demand that a NICU nurse do it. They are used to intact babies with even tinier penises (pl?) than your son has, and they know how to do it w/o retracting. In the even less likely scenario that your son requires any sort of surgery, make sure that you discuss cath/retraction with ALL the doctors/nurses involved. Sometimes they try to convince parents just do a circ "at the same time" (more procedures = more money!), which I assume you wouldn't want. And sometimes kids require caths for surgery, regardless of location. See above, and require a NICU nurse to place the cath.
Until such time as your son demonstrates UTI, or any other health issue related to having a single kidney (which should be sufficient for him, barring other complications!), I would not mess with it. Enjoy every moment with him, and your other children, and don't "borrow trouble" as my 92 year-old grandmother always says.
Hang in there! We're all here to help you, and support you, anytime.