Plaster, Chaux, Enduite et al

[Gabe]

I need lots of advice here...

I have just started stripping back the walls in our house (c. 1790s). I have removed all of the wall paper and in some areas not an insignificant amount of plaster and bits of wall etc, until I am left with a sound base from which to start repairs/redecoration. What I would like is advice on is the best approach and most importantly the correct materials to use to tackle the following scenarios:

1. Make good holes where powdery old chaux has been removed, to bring up to a level where the wall can be "plastered". Can you apply a tradional plaster skim finish over the top of chaux ?

2. In some cases there appears to be a layer of what can be best described as concrete. What is this likely to be and what is the best approach to repairing it ?

3. Patch existing skim layer, can you use plaster, any recommendations ?

4. Painting over the top of sound chaux finish, bearing in mind that this is not a perfectly smooth finish (not a problem) is there a particular type of paint that should be used, one that covers the little irregularities well and still allows the walls to breath.

I know that these questions are pretty vague, but any advice would be gratefully received.

Thanks

Gabe