Hi and welcome.
Weight will be dependent on your level of fitness. Tesco do a good value 5kg bell so if you've a local one it would be worth going in and having a practice swing and a shoulder press also (when there's nobody nearby to whack, obviously...) to see if this feels way too heavy. 5kg is usually the weight suggested here for people who are starting because it won't be 'grown out' of too quickly. I myself am still using a 5lb bell but have some health issues that have made me seriously unfit. So if the 5kg seems too heavy you could look at maybe a 5 or 7.5 lb bell. Argos sells Everlast kettlebells which are currently on sale, and you can pick up kettlebells of different sizes on eBay.
Make: as long as you get a cast iron bell, any make should be fine - many of them are coated with a sort of rubbery coating, but this is not to be confused with a vinyl kettlebell, which is a vinyl casing filled with sand. Vinyl kettlebells are *much* bigger, much slippery-er, and therefore generally quite unwieldy. In fact I bought the York and Davina kettlebell sets from Argos and returned them both because the vinyl kettlebells were just awful.