molleur – Good to see your build starting and it looks like you have a great donor car too.
I fully understand a tight budget and I would simply suggest having both a short and a long term plan.
If you are going to change the interior at some point in the future, I wouldn’t pick an exterior colour to match it now.
Instead, I’d suggest picking your favourite SWB colour scheme and going with that, even if you have a mis-matched interior for a while.
I’m sure I saw someone on this forum dying their coloured leather seats black, which might be a quick/cheap short term fix.
Good luck, Paul.