Dedicated line, how many outlets two or four?

Doesn't matter as much as conduit.

Jumia,

Go by wattage.  A 20 Amp line should be around 2,400 Watts.  In a typical home a 20 Amp line may be wired to four or more duplex outlets for convenience.

If you are running from 1 breaker, you would use 10/2.  If you were going to run 2 different circuits (on 2 phases) then 10/3 is convenient.

I put in 2 circuits so that I can put junk like switching power supplies for TV streamers on the other circuit.  I put six outlets on each circuit.  However, once you have a good poer regenerator, you'll find it is plugged in and most audio components are plugged into it.  Mine has 10 outlets on it and all but 1 is full.  Once you go down the high end power supply rabbit hole you'll need a lot of outlets.

I used 10/3 just as Erik describes above.   This has the added advantage of giving you access to 240V if you have a piece of european gear.

Just one item should be plugged in .. a very large power conditioner/generator.