The front track guards are cut down dozer blades (well spotted Spikyjames). They are off the old tank upgrade sprue, I'm not sure if GW still make them. I covered the gaps with some heavy foil from the neck of a wine bottle. They seem to be quite in keeping with the rest of the tank , sort of reminded me of the track guards on a T-55.
I've never had a problem dry brushing over Tamiya spray paint, just give it enough time to dry completely (overnight) and don't breath in the fume or you'll be coughing for a week! However I find trying to get a watered down wash to cover quite hard, as it tends to make the water 'bead'. On smaller models I've mixed up a wash and added a small (very small) drop of washing up liquid to kill the surface tension. On this beast I mixed up a wash from oil paints and white spirit, as it flows better over the paint. Only drawbacks to that are that it takes a good day to dry and is prone to handling marks whilst still wet, it also drys a little bit shiny.
The paint chips are only outlined in the last picture's and were painted on after the wash was dry and the whole model had been given a very light dry brush with corresponding coloured Vallejo paint. Just to lift the edges of raised areas and make the whole thing have a more Matt finish.
The chips are fairly straight forward, on the green areas I outlined with Vallejo 'Buff' and on the tan areas with Vallejo 'Reflective green', which is an almost spot on match for the Tamiya TS-61 'NATO Green' spray.