Regardless of whether the V5R3 client can be effective for your uses, I strongly advise upgrading them at least to V5R4M0 service level SI29771 for reasons described in V6R1M0 UPGRADE CONSIDERATIONS. It will be harder to upgrade them after going to 7.1.
From IBM i Access Connection releases, IBM’s statement is “The Windows client is supported connecting to N ± 2 releases”. AFAIK, that’s been the official stance for many years.
For PC5250, and for basic iNav functions at least, I think I was able to connect to 7.1. It’s been a while, though, so I can’t recall for certain. I wasn’t needing sophisticated access in that case.
Maybe discussion comments that contain links are delayed before showing. That would actually be a good thing. Tom