Bit of advice, may sound obvious but work out what percentage of your weekly income is taken up by van costs, insurance etc. otherwise you may think you're earning enough but in reality it's getting gobbled up with costs.
Looks like oiled veneer oak doors mate? Defo not the sort of thing u want plaster on so in future cover up. Lacquered woods are sealed so comes off easier.
You could sand them but will have to re oil after.
Pva and multi finish is what I do but I'd advise you to talk them into skimming the whole wall. I normally say a patch will be seen if you know it's there and the price difference won't be much by the time you've got there, set up etc.