RE: Scope Size
Normally the lower power the better the optics will be for the price point, and the clearer or brighter it will be in low light conditions.
I usually go for a 1.5-4 power or a good old fashion 3-9 and keep the power cranked down unless I need it. Nothing like shouldering a gun and having the scope cranked up too far to get on the target easy and fast.
Keep in mind I don't rifle hunt, I live in lower MI so I shotgun or ML hunt. 150 yards would be a long shot for me.
If you buy a decent scope you also don't need a big huge objective either. Keep the power level in a normal range and spend around 200 bucks and you shouldn't need more than a 32-40 mm objective.
Don't over look the value of a good fixed power scoped in 2, 4 or 6 power depending on where you hunt. They are normally more compact, lighter and sometimes more rugged.
Do not get a scope with an adjustable objective for big game hunting. You will not be happy with it. Get one with a fixed parallax in either 75 or 100 yards (most are 100 yards). Some better companies will let you order one any way you want it, or you can send it in and they will change it for you.
Paul