"... if we become friends" or "became" or "were to become"?

Solution 1:

You are suggesting a conditional (hypothetical) type of pairing. The usual example starts with the if phrase:

If we were to become friends, I would be very happy.

Reversed, it still holds it's form.

I would be very happy if we were to become friends.

The other sentences are certainly understandable, and basically mean the same thing. But there are some guidelines.

• I will be happy if we become friends.
• I would be happy if we became friends.

I don't know anything about the need for imperatives. The imperative might look like this:

BE happy if we become friends! (strange command)
Eat your dinner if you want to grow up! (common command)