"How Many Bicep Exercises do I Need for Optimal Development?"

In short, you really just need to progressively overload 1 bicep exercise consistently for growth. For the most part, bicep shape is determined by genetics, therefore, you should just focus on getting stronger in 1 or 2 bicep exercises to increase the size of your biceps. Big biceps lead to better looking biceps, regardless of the genetic shape. 

As a reminder, progressive overload means we're adding reps, weight, sets, or even frequency over time. Basically, just get stronger within a moderate rep range. When you can do 10-12 reps consistently with a given weight, increase the weight.

Now, there may be some benefit to doing a bicep exercise with the elbow behind the torso and an exercise where the elbow is in front of the torso. 

It's probably not a huge deal, but, if you're able, it's probably helpful to do 1 exercise for both positions.

Elbow behind the torso exercises include:

-Incline dumbbell curls

-Bayesian cable curls

Elbow in front of torso exercises include:

-Preacher curls

-Spider curls

-Concentration curls

-Traditional cable curls

Pick 1 exercise for each (1 for elbow behind and 1 for elbow in front) and do 3-4 sets 1-2 days per week. 

Adding a hammer curl variation may be helpful, too, but that's primarily a forearm and brachialis exercise. However, the exercise indirectly trains the biceps and creates a bigger arm.

You don't need to do 2 or 3 bicep (or hammer curl) exercises in the same session, though.

I do incline dumbbell curls 1 session and then concentration curls the next session. I used to do only incline dumbbell curls for a few years, but started alternating with concentration curls for variety's sake. It seems to have helped, but that may be more a result of having fun training a new exercise and the motivation that can be created from that.

I'll sometimes include a few sets of incline hammer curls after my bicep exercise for the day.

So a pull day might look as follows:

Pullups-3-4x5-10

Single arm rows-3-4x6-12

Incline dumbbell curls OR concentration curls-3-4x6-12

Incline hammer curls-3x10-15

Overall, I think this is a pretty good strategy to use for most muscle groups. Pick 2-3 exercises, rotate through them 1 or 2 at a time per session, and get stronger with each exercise over time.