The helmet, as everyone has said, is Marcher. The plate and maille you can (just about) get away with as a rich Wintermarker of the Steinr tradition, especially if you add furs and rich dark-coloured layered tunics with fancy trim. Bonus points for painting runes on it - Steinr are big on runes.
Your nation is a very important choice: most things happen within your nation, and most ‘plot hooks’ are open to groups within the nation. Your maille will fit for any nation, and pieces of plate for most (especially as you can wear them hidden and still gain the armour benefits!) - take time and choose a nation that you want to play.
The soft kit is the most important identifying factor, so really concentrate on getting that look right. You’ve got some really good basic kit already that works fine for monstering, and would look okay as-is in Wintermark (and maybe some other nations). Once you have decided on your nation, you can go through the ‘Look and Feel’ and work on modifying and accessorizing to make your national identity clear (e.g. with hats/hoods, cloaks/coats, trim and jewelry).