What are the optimal percentages for analog system

I would start with the best table you can afford. Usually you can get the arm in a package deal. Putting on an arm of your choice is something you might do once you have more experience with the gear.

Cartridges are small, fragile things, and unfortunately they do not get more robust as the prices go up. They also need to be retipped or replaced every few years, and even replaceable styli on moving magnets can cost half the initial cartridge outlay. So don't forget to figure in these replacement costs and your pain level for breakage.

A good phono preamp can make a huge difference, but doesn't have to be expensive. It's also the easiest analog component to change when you're looking for a different sound.

Figure out what cartridge you want, then find a table/tonearm that can handle it. Get the table first. When you have the money, get the cartridge. And when you really want to hear it sing, get the phonostage. Spend as much as you can on the table, it's the foundation of your system, everything else can be built around it.

I moved the RB300 arm from my Planar 3 to a Gyro SE, which was a huge upgrade in quietness (both less mechanical noise and less surface noise retrieval) and soundstage stability. The Rega arms are good enough to keep if you can get a good deal on an armless table (figuring in the loss of resale value of the whole table + arm).

I disagree with suggestions so far. With the TT you have and the cart, I would DEFINITELY get a better phono section.
The P3 is not a 'entry' table. Plenty of serious vinyl enthusiasts use it. The cart you have is OK
The table is a damn fine basic table, and if you like the sound of Grado, then you have a good combination there.
(you could easily go to a $500 to $700 cartridge later on your Rega P3 and be very happy all over again (if you get a good phono prepre.) Your current phono section is a really basic entry level one, and any used $500. preamp is going to bring your system to a whole new level.
To go for a top TT and cart with that cheap Bellari is foolish IMO.
Anyway, that is my suggestion.
I own:
Rega P5 with Benz Glider, to a Bryston 1.5/BBP-26
and
Kuzma Stogi S with Dynavector 17D3 to Audio Research SP-15 I use just for the tube phono section at this time, to the Bryston BP-26 also.
6,000 LPs.

This is a little complicated especially not knowing your budget and how far in your upgrading you are prepared to go in the near future. But I agree with those who suggest you get the best table you can. Good $200 cartridge will sound OK with $2000 table, $1000 arm and $400/$500 phono stage. With decent cables of course. You could also consider voltage stabilizer/conditioner or/and motor controller. Turntable can last for a very long time.
I personally would probably wait and upgrade everything at once and would spend at least 50% on the table alone.