If you're still in the out of the box Carbon then for sure a cart upgrade would be the next. All of Parasound's stuff is very nice, so I'd imagine you'd be good to keep that one until you get into the @ $2000 turntable arena.
It's a tough game to play and I expect you could ask 5 well-versed audio folk the question and get five different answers. I tend to keep my eye open on things on my long-term upgrade plan and if a bargain pops up, seize it. All my Acoustic Energy floorstanding towers that I've moved to (identical fronts and rears, AELite 3s) in the past 18 months have been used, original MSRP was $2600/pair and I got both for $500/pair. Schwing.
That Goldring cart is a really good deal at $325, not sure I'd go for it at full list price as it's more than the list price of the table. I think you have to decide how committed you are to a table upgrade and if you want one, how far off is it. If it's likely on the 10 year plan, putting a couple hundred bucks here and there into the table you have is a good idea, scratches that itch!
Phono upgrades are one thing I'd look used for too, and I'm guessing you got that Parasound used? I think the Zphono I have is the current equivalent of the P/PH? I got mine for US$125 demo model. When I score an upgrade, if I can get a @ $500 phono for $300 in the used market, hell yeah that's the way to go. With carts I like buying new, don't have a particular reason, it's just my personal preference. I'd need to know the seller pretty well to consider buying a used cart.
So yeah, I think cart is next. If you're happy with the volume you're getting out of that Marantz then you don't need an upgrade there, and when you do you could also just consider using the pre-outs and getting a dedicated 2-channel power amp. I'd look used for that too no problem.