If I want to use small guns as main weapon and energy weapons as backup what skill would be enough for energy weapons? 50+ or something? Thanks.

Personally I would make your Energy Weapons skill 75 at most and 50 at least

depends on your weapon of choice, if you use a shotgun most of the time energy weapons wouldnt do you much good. while i use a gatling laser, energy weapons and big guns are both at 100, small guns is still really low.

if you like small guns and have ammo for it focus on small guns, maybe a point or 2 in energy weapons.

I don't see much point in specializing in two types of distance weapon. Better to specialize in Big Guns OR Small Guns OR Energy Weapons, and back it up with Melee Weapons OR Unarmed. Channel the other points into Sneak or Science or something.