Really, the only character from Voyager that I'm interested in seeing again is Janeway. She'd be a good fit from this show because she is also part of the old guard that is no longer relevant to Starfleet.
If you‘re interested in Star Trek novels, the most recent Picard book The Dark Veil answers one of those.
He moved there during the Temporal Wars over 6 hundred years after the synth ban was a thing. I'd like to see how they interacted with him during the ban. I'm very interested in, but way behind on, them. We may be coming up on first contact with the Vulcans (or at least WWIII) by the time I get to that one and learn...
The only Voyager characters I like to see return in a cameo for a couple episodes are: Janeway would be fine. Tuvok Harry - would be nice to know if he ever got promoted after Voyager got home Tom and B'Elanna - curious to know if they were reinstated into Starfleet or resigned instead to live on Earth and raise Miral. Also if Miral entered Starfleet. Naomi - would be nice to see a grown up Naomi and if she entered Starfleet as well.
Why are people so intent on sabotaging this show that I like? Seven of Nine was the last iconic character Star Trek ever created. The rest of the Voyager crew? It doesn't matter how fond you are of them. They were failures. Janeway, Paris, Tuvok...failures. Sorry, but it's true. They utterly failed to capture the public's imagination the same way the TOS and TNG crews did. Janeway was the first captain since Kirk to run the risk of cancellation. When it began airing on UPN, Voyager floundered because the crew simply weren't good enough. They weren't charismatic enough, interesting enough, engaging enough. They were boring. They couldn't compare with what came before. Seven was the last time that (Berman) Trek was able to generate that spark of interest in the audience. You want to introduce Chakotay, Harry Kim, Neelix into Picard? Do you realize how crushingly awful these characters are? Do you watch any TV show other than Trek? Have you watched the Sopranos, the Wire, Breaking Bad? I can't see how you could tolerate characters such as Chakotay when you've sampled some decent writing. Picard has already taken Voyager's most popular, most successful character. Nothing else is needed. Let's explore the Fenris Rangers and the xBs. I'll give you your closure, though: Seven and Chakotay are no longer in a relationship because Seven is now being written by superior writers. There.
What is this hatred you spew towards me, you Talaxian Scum? Janeway was the best captain we've ever seen and they were far from boring? You want to talk boring, let's talk Enterprise. How were the crew of TNG so much more better than Voyager? Guiden was the stupidest character I've ever seen. Diana Troi? How would you feel if you were a planet that was immediately getting their thoughts read? Starfleet would never have an empath in the passengers seat when seeking out new life and new civilizations. Not if they wanted to make any friends. The first season of TNG was okay, the rest were just awful.
Just a friendly word of advise, the forum rules generally don't allow insulting other members, so you might want to consider not doing that.
As of PIC, Riker is on active reserve with Starfleet. He can be called back (or volunteer) at any time, and quickly return to duty. Which is exactly what happened - as soon as Riker found out what was going on at Coppelius, and that Picard was involved, he asked to be reinstated, and was immediately given a ship. Easy enough.