No high maintainance equipment; say goodbye to lascannons, plasma, multimelta, vehiciles more complex than rhinos and bikes, etc. Your weapon choices should be missile launchers, flamers and heavy bolters. Power weapons are out and even chainswords should be pushing it.
No terminator armour, no overtly special equipment.
Paint scheme, chipped, smashed, dirty, but still looking as if it's been maintained; these marines would look after what they had. Try making it look obvious that vehicles and armour have been patched up, but not in a ramshackle manner; you want poorly supplied marines, not orks. As for paint schemes, either camo colours, such as olive green or tan OR a nice regal scheme that's faded and mucky. The first suggests that they use whatever they have to the full effect while the secon reflects the chapter's sorry state.
Hope this has been helpful.