It is a fun game, yes i still play it despite my quibbles with it, premium ships are better ships, not massively but if you know how to use them they give you an advantage, i don't know about premium ammo, in wows you get flags, those flags give you perks like making your opponents guns disperse more, or yours less, visibility, manoeuvrability... as well as extra XP and so on., you can buy them, or win them.
I don't know how they do matchmaking, its not skill based or random, i seem to be permanently at least 1 tier above my own and that's not down to skill. I can have a good round but as i'm sure it does in wot it depends on your team mates, if you get people running off on their own or people running scared as soon as they are fired upon you might as well count them out because they are not contributing in a meaningful way, if that crap goes on and your opponents are organised its over in minutes.
Higher tier battles are 10+ each side, watchout for cloaked Destroyers they are like invisible assassins, and don't think because you're in a big fat Battleship you're immune to cruisers, while it takes you 30 seconds to reload some of those cruisers can do it in 4, they will rapid fire your fat arse out of the water if you're not careful.