Longtime JPN naval player here. I play RB and AB, but mostly in the former. Also lately have a preference for high-tier Coastal (4.0-4.3) due to imo favorable and enjoyable matchmaking/gameplay.
You do not need to get a prem DD to practice naval.
Bluewater rank 1-2 are relatively easy grinds. When choosing a ship to use in the lineup, I would recommend you use the JDS Harukaze (making a 4.0 lineup with various starter DDs and coastal) and JDS Murasame due to them possessing VT shells and radar which make anti-air quite effortless.
There is also the marketplace premium JDS Yugure, an ex-USN Fletcher-class (- 1 turret) which is a nice to have due to the same HE-VT and a decent armor belt, but is not required.
Many of the other DDs in the Japanese tree are workable to some degree, being fast, maneuverable, with good torpedoes (Type 93s), but they only have HE shells (and HE-TF), which are decent against non-US destroyers. IJN ships of note would be the following Rank IIIs such as the Akizuki due to her fast firing guns with good ballistics. There is also her sistership Hatsuzuki which you can obtain by playing 3 matches in WT Mobile - quite easy. Shimakaze is also an excellent ship, extremely fast, with her 15 torpedoes, but she is a squadron vehicle. (I actually prefer using her AB, where she goes 93km/h and has torpedo reloads, which I take advantage of when I purposely uptier myself with BBs)
Practice getting accustomed to both the US-type armaments of the JDS DDs, and the IJN ships. If you need to grind fast after getting past Rank III/IV, and you want a premium ship, I would recommend getting IJN Mikuma, a cruiser. She’s one of the faster cruisers, with fast firing guns, good shell choice, decent armor.
Notes for battles:
Spawn last - you avoid getting targeted by enemy ships
Avoid shooting first when too far away - same as above
Use plenty of cover
Don’t be afraid to spawn coastal if the smaller points are being contested
Floatplanes such as the F1M2 can be used to de/cap far away points - just make sure no enemy ships are nearby
Keep your head on a swivel
Avoid join in progress
Search online on how to set your mouse scroll wheel to adjust ranging