Slots and Ships

Yes, if you sell the ship, you will not need to buy slot again.

Unfortunately, it's impossible to buy a ship if you don't have free slots. You can sell any vehicle and free the slot. 

Maximum amount of slots in port is 12. It means that maximum amount of ships that the player can have is twelve. 

Yes, you will need a free slot as well as for non-premium ship.

The class of light ships (Destroyers) is cheaper than the rest in service and earns game currency the best of all, but the use of such equipment brings little combat experience.

Medium ships (Cruisers) are more expensive to maintain, so they earn less efficiently, but bring more experience.

Heavy ships (Battleships) are very expensive to maintain, but they get the most combat experience. It turns out that it is better to use light ships to earn game currency, so that you can then ride medium and heavy ones to gain experience and tournament points (trophies).

Also, depending on the class of the ship, the limit of possible activations of a particular type of modernization changes.

Destroyers - have a limit of 5 attacking activations (the remaining modernization are 3);

Cruisers - have a limit of 5 defensive activations (the remaining modernization are 3);

Battleships - have a limit of 5 repair activations (the remaining modernization are 3).

Premium tanks have following advantages:

- Are the best ships in their group;

- Have an increased limit of all modernizations;

- Earn more silver, experience, trophies in battle.