Tonearm mount to the plinth vs arm board vs rotating arm board vs isolated tower

Halcro, if your arguments are good, it’s really not necessary to be insulting.

The OP in this thread, is asking about an idler.

@kanchi647
The idlers are one of the crudest, oldest form of turntable, and with them comes.....(based on my personal direct experiences)

The most vibrations, least isolation, the most noise.

That's what you are dealing with.

For these reasons I would recommend you try a design that works to eliminate those three (at least) design symptoms.

If you look above, I said pretty much the same thing. 
But "crude" does not equal "inferior". 
Take the first ten vehicles featured here  https://www.townandcountrymag.com/leisure/sporting/news/g2165/best-vintage-cars/
Each and every one is "crude" by today's standards and yet they are-imho-more desirable and more "worthy" than anything available today at any price. You can argue all you want that a top Tesla is far more "precise" (think "accurate") but where will your Tesla be in ten years. Likely in a scrap heap. 
As crude as they may be, idlers are built to last and capable of giving incredible amounts of joy and pleasurable reproduction of music in the home. They possess a color, more-so than top direct drives, but I would rather have the slight color they provide. 

I agree with @halcro , it is essential to isolate the tonearm from the platter bearing and the motor.

I also agree with @atmasphere , it is essential to have the tonearm rigidly connected to the platter bearing.

I also agree with @lewm , bolt the tonearm to the plinth if possible, but compromise as necessary.

There is a material which is highly rigid, on the same order as aluminum plate, which is also very highly damped. That material is panzerholz. I built my platter board out of panzerholz and glued a layer of carbon composite to the top for further rigidity and constrained layer damping. Then I bolted my tonearm to the platter board.

Bearing is all air - high pressure amorphous carbon bearings in three dimensions. Bearing is grounded by offset steel columns connected through panzerholz blocks from (slate) tabletop to platter board. Platter bearing noise is nil.

Outboard belt drive with a flywheel allows excellent isolation of the motor. I say, "Let's have it all !"

Actually, a huge "THANK YOU" to all three of the above, who guided me to the above design. Also to the late Tom Fletcher. I certainly could not have done it without you.

Fantastic input from all the members. Challenging each other but I am learning a lot at the same time. I am still thinking of how to handle this..