Personally, preflop I would open to $1 (4xbb) from MP2. Imo it just makes more sense that when you have a tighter range to be building the pot. Well in the Early/Middle positions your range should be tighter than in LP. This is why I raise 4xbb + 1bb per limper from all positions but CO/BU. However, 3x is fine.

Shoving is way over doing it. You need to think of the villains possible ranges. What hands are you ahead and trying to get value from? What hands are you behind and trying to minimize your losses against? A shove on your part here folds out the majority of the hands that you are wanting to get value from (that is hands you are ahead of).

Now a raise is definitely, and I would raise to something like $8-$9 or so. Villains will still put it in with Pair + flush draw, Flush Draw, two pair, etc type hands. Hands that a shove is likely to fold out.

When you raise here and villain shoves, your calling. A flush isn't the only hand villain could do this with, and even if that is so you have 10 outs to either boat or quad up.