The first and most important question is WHY?
If you are going to make all these upgrades, why buy this table to start with, and why keep it now. The Ortofon 2M Black is about £450. That seems a lot for a turntable that is basically £230. And yes, I know your particular model cost more than that with the Phono Pre-amp and SpeedBox, but it doesn't change the fact that it is all based on a £230 turntable.
SuperFi.co.uk - Project Debut III Phono Speedbox (£344)
The Project Debut III Esprit does come with an Acrylic platter, so I would suspect you could retrofit your existing turntable with that for a fair price. To know for sure, you would have to contact Project.
As for the Cartridge, I say either get the 2M Blue or sell what you have and just get a better turntable.
The Project Xpression III with acrylic platter, and 2M Red is about £450, but could easily be bumped up to the 2M Blue. The 2M Blue on its own is about £150, and the 2M Red is about £80. So add the difference to the price of the turntable.
Really, it gets down to budget. How much do you have to spend, if you are looking at the 2M Black then you must have £500 or more. I think that money would be better spent on a new turntable.
However, there are some reasonable upgrades you can make to your existing turntable. If you insist on the Acrylic Platter, then check with Project and see what the price is. Again, there is a Debut III model that does have an Acrylic platter so this isn't too far fetched. Then, upgrade to a cartridge in the £150 to £200, such as the 2M Blue, if that appeals to you.
Ortofon 2M Blue - Google Search
Grado Prestige Silver - Google Search
Grado Prestige Gold - Google Search
Ortofon 2M Bronze - Google Search
SuperFi.co.uk - Project Xpressions III Turntable (£444)
Project Xperience Turntable w/ Ortofon 2M Blue (£774)
To go much beyond that, to be considering £500 cartridges and replacement tone arms, in my mind, just doesn't make sense. Far better to just buy a better turntable.
It would also help to know what the rest of your equipment is (amp, CD, speakers, etc...)? That would give us a better sense of proportion for this proposed upgrade.
But personally, I don't see sinking £1000 into a £200 turntable as a wise move.
And finally, though mentioned before, what is your goal? What is your purpose? What do you hope to gain or change that you don't have now?
Just one man's thoughts.