Standard disclaimer: This is all my own opinion based on my experience as a professional bass player. Have a nice day.
A bass player, the most important person/persons in the group? You may not think so (especially if your a lead guitarist) but they really are. So you should know what you need to be a bass player.
Bass players are renowned for being the quiet one in the corner bobbing along to their own grooves (beard recommended but not essential), but some are different. This covers the topic of over playing and showing off. I was guilty of this once upon a time. Basically your bass player should be in the background as said as above but with equal input to decision making, not out at the front slapping the funkiest grooves on your well polished smooth jazz track. That said everyone in the band should be able to have their time to shine. To round off, your looking for a reliable workhorse of a player who can play over all changes with ease (and without the attitude) and be able to hold back for someone else to take a solo.
Everyone has a list of what techniques they can do and how fast they can do it (I can slap the most ridiculous syncopated lines at 3000000 bpm ) Is it necessary? In a way yes but in a way no. As a professional bass player you are required to play what is put in front of you with all the techniques included, it is a given. Does it happen a lot? No, out of the hundreds of tracks I’ve played on I have used only 3 techniques on three tracks that would be considered different to conventional bass playing. Techniques are a must but keep them to yourself until the time is right.
As a music educator I see more and more players coming through the system only being to read tab, this really annoys me. By reading tab instead of music what can you achieve? Not a lot and not a lot of work either. I strived for many years to be able to read the bass clef confidently and I believe it puts me ahead of players who cant. It is an essential part of your work. Having an advanced grasp on all theory will undoubtedly improve every aspect of your playing. New compositions, new parts, new chords for you to play over. It’s all needed to be a confident performer and bass player. I regularly receive scores which just outline the chords and basic melody for me to compose a bass line over. Without my knowledge of theory I would be in trouble.
A big subject. Does it really matter what bass you use? Yes and no. If it works properly and doesn’t hinder your playing ability that’s great! Below par instruments are just a big no. It doesn’t have to be an expensive instrument as long as it works. Some situations it is required to have a high end instrument and that’s just the life of a musician. I mainly use 3 basses in a rotation of what is needed for a session, performance or even for each song, but make sure you have options to broaden your capabilities i.e. 5 string basses, fretless etc. The same for amplifiers, I use a bass workstation for my own work or live performances but for larger performances (very rarely) I will use a larger Trace Elliot rig. As long as it works, gets the tones you need and will work in the scenario its great. Effects, I use a few but very rarely apart from my sub bass octave. They can be useful and sound great in the right situation. Just experiment and see what works but don’t start using your new wah pedal right in the middle of your cover of Fly me to the moon.
So this is just my little piece about the basic essentials you need to be a competent bass player in today’s day and age it’s all a bit rubbish really, because it depends on the person and the group and everyone’s different but this got me to where I am today along with being lucky!