You don't need a 5, but they have both advantages and disadvantages.
Advantages:
- Lower range
- Added flexibility in fingering positions
Disadvantages:
- Heavier
- Wider fingerboard
- Different Orientation
Different Orientation is key to me. I am a long time 4 player and resisted 5s because I have short fingers and because I always have oriented on the E string. Now I am playing more 5 because the band I'm in tunes down 1/2 step and I refuse to loosen my string tension (that's another long discussion) and I've struggled with hitting the right string. I've been at it now for about 5 months, so it is getting easier and I hit the wrong seldomly now.
I do like the availability of alternate fingerings.
The only issue now is I have to readjust my brain when I use a 4.
That is my experience; however, it may be different for you. Since you are a relative beginner, you will have less to unlearn. It is like a small child growing up in a multilingual environment. It will learn both languages and not get them confuse. But, for an adult, learning a new language is a struggle.
HTH