So is the point of the premium vehicles to earn credits? Do they have other advantages over their non-premium counterparts?
Does that mean it's prob not worth it for me to get premium vehicles until I'm pretty committed to playing this game long term?
Originally the Gold tanks were weaker than tanks of the same tier however with the introduction of the Lowe and Type 59, this seems to have been blown out of the water.
The Lowe has some drawbacks but it isn't bad compared to the other Tier 8 tanks. It can certainly hold it's own against any Tier 8 heavy although it will suffer pretty heavy damage.
The Type 59 is scary because it has a high top speed and such a low profile that a lot of people bounce on it. It suffers from an ammo rack issue (liable to be damaged or outright blow up, though I've never been 'racked' in it or suffered many ammo rack damages). It can hold it's own against any other Tier 8 Medium, however I think the Pershing should beat it more often than not. It's also lacking in acceleration.
The main 'good' thing about the Lowe and Type 59 are that they earn BOATLOADS of credits. With Premium account and a reasonable exp win, I can turn up with 60-70k credits pure profit. That's after taking off my ammo costs, repair costs and consumables.
Each tank has drawbacks. The Lowe has relatively paper thin armour except the turret, acceleration is terrible and as with most German tanks it has transmission parts in the front which can mean engine damage or fires from front penetrations.
The Type 59 has poor acceleration and a flimsy ammo rack. It also doesn't keep it's speed very well when climbing hills or encountering rough terrain.
I can't really provide a recommendation to you. I've played WoT for a year (inc closed beta) and so I've paid accordingly (multiple months premium, Lowe and Type 59). In short I've paid about as much as I would if I'd played an MMO for 12 months or purchased a couple of titles at launch and only have them last 4-10 hours
Premium account and Premium tanks only really help you earn exp(account)/credits(account/tanks) at a faster rate than you would elsewhere. If that is important to you and your enjoyment of the game then I'd recommend Premium account certainly. Splashing out on a Type 59 might be a bit of a big purchase if you end up turning your back on the game in a few weeks but it is a permanent feature which will be there as long as your account is.
For me, I've loved having my Lowe and Type 59. Running them one after the other I can rack up a large amount of credits and that helps me purchase new tanks, old tanks (that i've sold in the past to buy new tanks), run every tank with consumables and buy specialist equipment such as the Gun Rammer or Vertical Stabiliser for my tanks.
Re: Garage slots. If you buy some gold, I would personally try to juggle around with just 5 garage slots until they do a special Garage Slots sale. They tend to go for 150 gold instead of the standard 300 on a slot sale.