I have table with 5 columns each column length varchar2(4000). This table will have approx 150000 rows every year. I am planning for creating a seperate tablespace for this table because of its row size .
While calculating rowsize i did it as below

5* 4000 + 15( Column overhead of 3 bytes because col length is more than 250 bytes) + 3 (Row overhead) . 20018 bytes per row

20018 * 150000 = Approx 2.8 Gig.
I have enough space. Is it a good idea to have a intial extent of 2.8 gig size ? Please advise