Varnish Question (oil painting)-???

[Noumenon]

I have a couple of questions regarding use of varnishes.

1.
1. What would be the best (final) varnish for oil painting ?
(standard stretched canvas, classic glue primer & gesso,
oil paints, medium: turpentine)?

Naturally, when painting's finished 6-8 months ago.
(Some areas of canvas may have received slight treatment of
retouch varnish during painting.)

I incline towards using KETONE varnish (but there are no serious
reports as for durability and compatibility of this varnish).

Does anybody know anything about SILICONE varnish (presumably
most stable and lasting, as it's used by conservators? No?)

2.
2. I didn't find any coherent information about few layers of
different(!) varnishes.

Does anybody know how it works?

Say, if a painting was varnished with dammar varnish some
5-10 years ago: should it be removed before ketone varnish
(or synthetic varnish) applied?

What would be typical approach?

Do people use special waxes for coating, I wonder?
Or it's obsolete method?

Could some veteran share some experience in this regard?
THANKS!

Weaving the Conundrum
-=| NOUMENON |=-