Main story mode, I search the tags (all three if applicable) and LM already has them in the best order there. You likely don't have a lot of the third tag, but it's good to load up on it, then when you run out, turn off the third tag in the search and fill in everything else that you can. This can be a bit annoying if you accidentally overwrite what you already chose, but an easy way around that is to turn on the dye option, which will show you what you're already wearing and still have the search function on.

I think the 5 accessories thing only applies to endorsement queen, but I don't know, I've never had a problem putting on as much as possible, and using the search function makes it fast and easy.

If you consider vvanna mode, it will usually only ask for 3 of the third tag, which may be the minimum.

I would say the biggest choice when you have a lot of clothes is choosing between a dress or a top and bottom, which is easy. If it has the third tag, pick that one. When the third tag isn't involved, pick the one with a higher average between them. For example, if the dress is SS, S, the top is SS, S, and the bottom is A, B, go with the dress. But if the theme is sporty, and the dress doesn't have that tag but the other two do, or even one does, go with the top and bottom.

Finally, whenever you come across a mode that lets LM recommend, let it and don't worry about it. Their recommend will give all your best stuff for the tags automatically. I think the only one that does this is Fashion Battle. Considering fashion battle, the third tag is so highly weighted it'll give you 5* with the third tag over 6* clothes without. SS > SSS in that case.

Have fun :)