I bought a carbon telescope with a view to restoration. I am thinking of buffing down and recoating with XCR Epoxy. The telescope was obviously left outdoors at some point, some of the bolts are rusty and the Aluminium end caps are bubbling under the paint (powder coat?). I have attached pictures of the carbon, and was wondering if anyone could say what the white marks are? It must be some kind of water damage i think, and thought it might be best to get a second opinion of what, if anything, can be done about them before actually doing anything. I think I will re-coat anyway as there are loads of pinholes.

Visually. By the amount of of pinholes. From a technical point of view it will be fine, especially since there will be only little and mostly static loads in this application.
The lines are a common pattern of bad wet layup. There was plenty of air trapped under the first layer, and it's stretched out along the brush strokes.
From what I can tell this is only a visual defect. And before you start sanding off the gelcoat, I would like to say, that it takes some practice to get back to such a smooth, shiny surface. Cylindrical objects are even more difficult, since you will easily detect every plateau from the sanding process. Plus polyester surfaces are a dream when it comes to polishing. It is difficult to get epoxy resin to that grade of shine. It might be, that you will end up without the pinholes, but with a less pleasant look nevertheless.