As you are in the UK most of those in the US are not going to understand what we have here in the UK.
Loaning (for those in the US) is essentialy a free lease. Snizard if you are paying the horsesowner to use the horse then you are leasing.
Anyway UK inhand showing all classes are pretty much the same.
You will need some light coloured trousers (most people wear beige with a dark horse),
Jod boots or walking boots that you can run in.
Tweed jacket (always tweed inhand)
Brown leather gloves
Hair in a bun,
Navy velvet hat with flesh coloured straps,
Brown show cane.
Generaly you will need a plain hunter style bridle for inhand classes.
Horse should be immaculate and as he is a friesian have a lovely long flowing mane and tail free from knots.
A very good site for information is Front Page
they also have a very good forum, you have to pay to join but there are a lot of proffessionals on there who will freely give advice.