New TT or upgrade cartridge/platter on Project DC

Its true, a turntable rewards tweaks like you can't believe. Your Project table is plenty good enough for you to know you love vinyl. Which is really something considering its a very entry level table. Getting more involved with setup and adjustments like effischer suggested will pay big dividends now and even bigger ones later on when you do buy your next table because you will know so much more what matters from actual experience.  

The truth is what you already have is more than good enough so that all your most cost-effective upgrades right now will be tweaks, accessories, and adjustments. I'm not just talking about the turntable either by the way. I mean all of what you have. But that is only considering sound quality and sound quality alone. Because a lot of the most effective improvements are invisible. But how things look matters too, and more to some than others. So really it turns out that as important as it is to know the components its equally important to know yourself. 

You're coming from digital and have enough experience now to know you are into records. Great. Turntables and records are a whole thing unto themselves. The good news is there's no right or wrong. Any of the things you are considering, new cart, platter, whatever, they will all open up a new window in terms of sound quality. No doubt. So no worries there. 

What's different and pays to think about with turntables is they are (or can be) a very long term investment. Mine is more than 15 years old and is still going strong and far down the list of components I would like to upgrade. https://systems.audiogon.com/systems/8367 There are lots of very old (vintage) turntables still very highly regarded. My point is a turntable can be a much more long term buy than just about anything else. 

So that is one upgrade path, to save until you can afford a level that will last you a good long time. But remember there is no right or wrong. Another equally good but different upgrade would be to plow as much as you can afford right now into a really good cartridge. 

The big advantage going this route is huge immediate improvement much greater than you could ever get with something like a better platter. If you go this route I would highly recommend something like the Soundsmith Zephyr MIMC https://sound-smith.com/cartridges/fixed-coil/zephyr-mimc-%E2%98%86 While $2k I believe all Soundsmith are 25% off right now. Ordinarily I wouldn't recommend putting a lot in a cartridge right away because they are sort of disposable items and I like to think more long term. But Peter Ledermann will rebuild these and for a good enough price you can consider them a longer term investment. 

Last thing to think about, the phono stage. Equally as important as all the rest. What are you using now?