How to do the beams?

One of the questions we are considering (as an exciting change from fretting about what the floor plan should be) is how we will finish the beams in the upstairs rooms (spare room and either 2nd spare room or living room depending).
At the moment they are just rough as they were cut, some parts have been painted but it has worn off a lot and they are quite water stained (not to mention covered in dust, dirt, the odd bird/bat dropping and cobwebs).
The only part of the roofs woodwork which will be visible is the A frame (see red lines), the rest will be covered by insulation. We are planning on the stone walls being exposed (painted at the moment but we will remove that and re-render) so the whole A frame will show including the bits that go in to the wall (where apparently they connect to the floor beams and stop the walls being pushed over by the weight of the roof - who knew?)

Red is what will be exposed

We are not sure how best to clean and finish the wood. I would like something which is possible to dust in the future (despite cleaning not being a favorite activity it does get done occasionaly and a rough finish would be annoying on the odd occasion we do try to clean) and we need to do something about removing some of the staining. Whatever we do they will be sprayed with Xylophene to treat for woodworm and other wood eating insects (we don't get termites here which are a bother in a lot of France). I would then like to be able to oil or wax (not varnish). 
Reading what various other people have done the most common thing is to 'sand' with an angle grinder and then finish with wax or oil. We have 4 to do (plus whatever we end up with in the bedroom - still under discussion what is structural and what not) so probably doable. I would guess we might need to do something about the water stains too, possibly with oxalic acid (I was reading about how to cure sheep skins for sheep skin rug when I read about this) 
Bright ideas welcome...

Paint and water stains

Dirt and water stains

This is a relatively clean smooth bit

They look better from a distance and with the flash

Will be lovely when cleaned up