Leaflets come in all fancy shapes and sizes, from a standard A5 to a modern square, or even a complicated cut out.
It's not just sizes you have to choose from but paper weight and finish. I'd always go for a thicker leaflet for a tactile and
professional feel. You'll have the option of several finishes,
depending on which printer you choose. Such as gloss, matt, matt laminate, uncoated, recycled. For a standard leaflet, a matt finish is a great modern edge, add a laminate to that for longevity (harder to tear). Contact me for advice on an ideal set up and design for your leaflet.
I don't offer a printing service, but can help you navigate the minefield of paper weights, finishes and paper types.
Starting with how your brochure is bound. This means, how is the spine of the book going to be stuck together. There are a few options: Perfect bound, Loop bound, Wiro Bound and Stapled. If you have enough pages, I would go with perfect bound (like a regular magazine is). Loop bound is held together by printing the book on A3 pages and making a couple of holes down the fold and putting just 2 metal loops in, a bit flimsy for me.. Wiro, is essentially lots of metals hoops scaling the spine and stapled, well I think that one might be easy!
Pages & Sides: You can only print booklets / brochures in multiples really, these are 8, 12, 16, 20 etc etc, these aren't pages, but sides and include the front and back cover.
Type of paper. There is Silk (has a slight sheen), Gloss (shiny), recycled (often stippled), some offer a 'natural' paper (uncoated and untreated, so is off white) and finally general uncoated (cheapest option usually).
My favourite printer i've come across online is Mixam.co.uk, i've used these guys for a long time without a hitch. I also used my local printer, it's great that you get to talk through ideas on printing if you don't know exactly what you're after.