Some years ago, I played in a band with a cellist. He played an electric 5 string cello in this particular band, but he was a traditionally trained classical cellist and played the normal instrument in various orchestras in the area. He was also a pretty competent keyboard player (he also wrote extensively on the subject of electronic keyboards and synths).
He played bass just fine and I don't think he had too much trouble moving from one instrument to the other.
As BruceWane, mentions above, you are already a musician in the sense that you know scales, rhythm, the idea of technique, and how to develop it (on one instrument at least), so I would just think of it as another instrument and learn it on its own terms .. normal bass tuning, and reading bass clef.
I would also point out that while sight reading is a very valuable skill; for pop music, the ability to read a chord chart and understand the basics of the music you are playing (groove, style etc. ..) are probably just as valuable, unless you want to become a working pro and expect fully notated charts to be available on sessions. In 45+ years of playing, the only places I ever saw fully notated parts were on Big Band gigs with a book, a small handful of recording dates and a few fusion gigs where the song writer had mad orchestration/charting chops. Sight reading for stabs and specific figures, and the ability to execute directions like "straight 8ths rock groove" over a chord chart, and a good working knowledge of structure directives (repeats, DS, DC, DC al coda etc ..) would be more practically useful. Again, thats IMO/IME.
but most importantly
enjoy!