Upgrade Path for Deck

My system is CAT SL1 Signature, Lumley M120 monos, ProAc Studio 150s.

My front end is Michell Gyro SE, Incognito Rega RB300, Ortofon FL25. I bought this about 18 months ago, in my desire to get back into vinyl. It was a good decision as most of my listening nowadays is on the black stuff.

I would like to upgrade, but would like it to be my "final" upgrade. My intended upgrade is Avid Acutus, SME or Triplanar arm, Transfiguration temper cartridge; which all costs a lot of dosh, and I cannot do it all at once. In fact i will need to do it in three stages.

Question is what should the first upgrade be, and then second and finally third. I love the sound of the temper and would go for this as the first upgrade, but would it be a bit over the top for the RB300 arm? My dealer suggests the deck should come first (incidentally, the most expensive of the three components), but would the RB300/FL25 combination let it down? Or should the arm come first - at least I could optimise the set-up of what i already have?

Really don't know what to do - so your advice would be most grateful - My aim is to generate a list of pros and cons for each option, and to come to a decision from that.
The generally accepted order of importance in an analog playback system is: turntable, arm, cartridge.

When you improve the turntable, the existing arm and cartridge will provide a higher level of performance than they previously did on the old deck. So you get an upgrade in all 3 areas at once.

When you improve the arm, the existing cartridge will perform at a higher level, thus yielding upgrade in 2 areas at once.

The cartridge improvement will yield upgrade in one area.

Of course, this is based on the assumption that the upgrade you make is truly an upgrade, and not a sideways or downward move, which sometimes happens.

So, in my opinion, doing the TT first will give the most results, even though it will likely cost the most.