Nope no guitar experience is needed. It helps a little, though having experience on drums is just as helpful. Bass and drums got to be tight to sound good.
As for learning the starting point on bass is much easier to learn than guitar. Your initially just following root notes on the guitars mostly and bridging the drums to the guitar(s). Bass is very right hand technique while guitar concentrates more on left hand technique. With a bass you have to squeeze more sound out of each note as your not doing as many chords and far less complex chords. So long term it's not easier to be a good bassist than a good guitarist. Short term you can become a novice bass player far faster than a novice guitarist.
Learning guitar helps in that by knowing the chords the guitars are playing it helps you decide which are going to be your key notes and how you'll drop off for harmonizing and adding to what they are doing. Initially the top note they are playing is your key note, the root note. The top note can be an open string sometimes so don't just watch where the highest finger is being played, check for open notes being added in as well.
From there you can add in short hammer ons, walks and other stuff to decorate your basic bass line. Then as you start getting better your interacting with the guitars rather than just following them. From the start your interacting with the drums.
Just like on drums, often bass lines are improvised on the spot. Unless you develop a signature line or the bass is carrying the melody in a song you have lots of room to play. That's one of the most addicting things about playing bass in my opinion. I can sit in with a band and in a few runs through I'm playing a coherent bass line. All I'm worried about memorizing is the changes and the basic structure I need to carry for most tunes. The rest I make up on the spot as I get to that part. If I find something that just really adds to the song I cement it in and play it that way every time I play that tune. If bass is carrying the melody well then your stuck with doing pretty much exactly the same thing. You can throw in a few things here and there but if your chained to the melody your nailed to a bass line for that part of the song.
Depends on your genre also. Rock, Metal, Jazz and Blues leave a great deal of room for bassists to improv. In those genres the bassline is for many songs the most promient instrument at times. NIB for example. The guitarist can forget to turn his amp on and the song goes right on without em. There are lots of Rush, Iron Maiden, Primus, Loverboy, Led Zep tunes where the bass really drives the song.
In Country your relegated quite a bit. Bass lines are more walking than carrying the tune. It's very rare for a bass line to carry the melody in a CW tune. Almost unheard of for it to be the promient instrument in a CW tune. Pop tunes the bass lines tend to be aggressive but static. You don't have the wiggle room you would in other genres.
As for strings 4 of course is the standard. 5 string basses offer lots of advantages and I've seen 7 string basses. Even picked one up and had no idea how to play the monster LOL. The neck was so wide I was really struggling to reach many notes. Most bass players go with 4,5 or 6 string basses. I recommend starting on 4. The 5 string basses offer extra challenge and if you get dependent on that thump from the B string it'll retard your development as a bass player potentially. Best to learn how to create a punishing sound without resorting to just a B string thump first. Then you can add that easy thump to your sound after you've already mastered the 4 string.