Revivng a Series 20 table and arm

I am putting my seldom used Pio Series 20 PLC590 table and PA1000 carbon fiber arm back into regular use. I has sat little used in recent years partly because it has a vintage 1991 AT OC9 moving coil cartidge and my current (temporary) Yamaha receiver only has a moving magnet phono stage. ( I am moving up to a separate amp/peamp combo in the near future.) Here are some pics:

I still have a DECCA carbon fiber record brush, ultrasonic stylus cleaner and Audio Technica Stylus Cleaning fluid and I just bought the AI record cleaning fluids. Also, I still have the dust cover in good shape, but I removed it before the photos. I have ordered a Besttractor alignment tool from Yip in Hong Kong and have a digital scale suitable for use in setting the tracking force.

1) I need to replace the cartridge. I am debating over going with a new AT OC9ML moving coil cartridge and get a separate phono preamp such as a Cambridge 640P or go with an AT 150 MLX moving magnet cart and maybe still get the Cambridge Audio 640P a little later on. Or do you have other suggestions.

2) Is the Cambridge 640P the most appropriate preamp if my budget is under $500.00 ?

3) My tone arm uses a cable with a standard DIN fitting but the cable appears a cheap and a bit basic. I am considering replacing it with the FURUTECH AG-12, but am open to other suggestions.

4) I would like to build an isolation platform, but I am torn between a maple butcher block platform and a sandbox platform. The PLC-590 had flexible spider shaped rubber cushions between the chassis and the circular feet, but I think the foot mounting bolt still transmit some vibrations.

5) The platter is about 4 pounds of machined aluminum and very resonant, but there is hardly any room for something like plasti-clay due to the tight clearances between motor and plinth. The rubber platter mat does a fair amount of damping on its own. Any alternative damping ideas, or am I just over obsessing here?

6) Any other tweaks or suggestions come to mind that would improve performance at moderate cost?

All suggestions are appreciated.
1) This is a matter of taste, both are fine cartridges and sound very good.

2)Survival of the fittest means that most of the under $500.00 phono preamps on the market are just great. The Cambridge is a value leader and the current darling of the budget internet set, but depending on your choice of cartridge, and your taste, you may prefer another phono pre. For instance, with the 150 you might like the smoother Gram Slee 2SE, at more than twice the price of the Cambridge, and MM only. BTW, I have a Cambridge 640P as a backup phono pre, so have no predjudice against it.

3)This may be a worthwhile upgrade. I am speculating here, but from the pictures, that headshell looks very resonant. You may want to consider a nice aftermarket headshell such as the Sumiko, Yamamoto or other designs.

4)I have not had good luck with sand boxes, though other's have. You can mock one up with a cardboard box and a slab of wood to see if it is going to work. Just because you feel that vibrations are making it to the plinth, doesn't necessarily mean that they are not being dealt with.

5)Yes, you are.

6)Some rigs sound better if you take out the little rubber gasket on the headshell. Others don't; you will have to adjust overhang if you do this.

Be careful with that ultrasonic stylus cleaner, some report adverse effects on the suspensions of some brands of cartridges.

A good record cleaning machine will probably have the greatest benefits for sound quality and longevity of your records and stylus.