[Radioroslyn]

Let me see what a can answer for you.

<I bought here some meters of cotton braided wires of different colors to replace all wires

Good move. Two things to consider. Rating of the insulation as your set has about 300vdc running around in it. On the power transformer the two hv wires have about 700vac between them. The other consideration is the gauge of the wire. Needs to be able to pass enough current for the heater circuits. General recommendation is 20ga. I just mention these in passing your probably fine with what you have purchased.

>The rule of 20% tolerance is for all components or just for resistors?

When the set was made 20% was what used. Now days resistors 5% or better. The foil/paper caps I wouldn't both to test just replace. Micas I would leave alone unless there is a problem.

>The guy in the electronics show told me that equals to 600dc volt rating, is true or I have to search 630v capacitors?

The AC rating is about 1/2 of the DC rating so you should be ok.

<many wires are like this or are like glass when I bent them

Generally I don't go out of my way bend wires as they are brittle. On the later Philco models (1939-42) and a lot of other models rubber covered wire was used. The rubber coating turns to dust when looked at funny or touched. These set usually require a good bit of rewiring to get them back in good order.
When rewiring be carefully about wire placement as some wires don't get along being near others. In other words layout can be critical. It can cause some circuits to not function or oscillate. Take pics and notes on the original wiring. Some folks will try to "neaten up" the wiring by rerouting some wires only to have caused problems in the end.

> electrolytics cans were looking nasty and leaking some kind of acidic stuff that corroded the chassis.

Some will have a white powdery stuff at the top and or bottom. As far as I know it's not particularly caustic washes off with a little soap and water.

GL