A Paddletail was my first ever newt, threads like this one always make me kind of nostalgic.
I would recommend a 10 gal tank as an absolute minimum(I know many people say 5 to 10) as you may be suprised at the size a healthy individual can achieve and they're quite active.
One thing I cant stress enough is that paddletails are not community animals, they are very aggressive and territorial, even with fish. I personaly am not against species mixing overall, just not with this species.
Currents can be achieved with a filter, depending on what your using, or a small submersible pump, depending on how much money/effort you want to put into it. I eventualy kept my first one in a long tank with pump, tubing and a cork bark structure so there was a still pool and a constant gentle current.
Provide hides and decoration so it can conceal itself, they rarely leave the water if healthy but you should give it the option. A floating island or just some wood protruding from the water is sufficient, chances are it wont be used. I used piles of large rocks and split cork bark curls.
I've found floating plants to be best as paddletails are quite strong and I've had them kill/dig up rooted plants. Java moss, elodea, milfoil and the like are all suitable.