I would suggest, along with all the other excellent advice you have be given here, not to forget your OP shop sources for things such as ties, waistcoats, buckles for daywear belts, kilt pin alternatives etc, Whislt you have been given a generous amount of money to equipment yourself. I would suggest that you don't go the whole hog in one go. In an earlier post you said that your have dressed from OP shop clothes in the past, so don't loose that valuable source.

As has been advised, get yourself the essentials, wear it a bit and find the style that suits you, then build on that style.

As for daywear shirts, I like the the tattersall style, with a tweed tie.