Given it's your first band, I'd say count all the bars.
Then, as Alparrot said, once you get more experience, you'll learn when you need to count and when you can just feel you're way through it.
Does anyone here actually count out the number of bars as they're playing so they know when the next part is coming?
I've been in several bands where there were backing tracks, and I'm playing to a click. In those cases, it's important I know exactly what bar I'm in at all times because the band is relying on me to make it all line up with the backing tracks, and play the right cue to go into the next section. So yes, I'll count.
In other situations, probably not.