it depends on your approach, do it at a nice eacy pace and while initially getting the car roadworthy dont go overboard, mine needs a new interior, and hood but i've so far concentrated on the welding and getting the car mot'd, the rest will come in time, buy too much in one go and keep count and you will see the drawback of classic ownership in that you very rarely will be able to get back in value of the finished vehicle what you have spent to do it up.
unless the cars original seats were totally shot then replacements were not really a priority, twenty quid would see you sat on half decent seat covers and money saved there could get the welding done for the mot etc.
pace yourself and prioritize structural mot able work before the pretty stuff, will cost less initially and will get to the same result just maybe a little slower....
just look at mine...lol, it might see paint this year but mines been in my hands just over a year, but so far the work has been welding and new subrame and brakes etc...... but its getting there.......
the project at birth, watch it evolve...I hope...