Should I Change The Alternater If It Needs To Be Removed?

If he wouldn't charge any extra to slap the new alternator in... I would go ahead and have him do it. Likely your current alternator is getting tired and will fail soon anyway. Probably cost you about $300-$400 for the new alternator. But you would save about $200 on labor if he put it in for free.

before your mechanic changes your oil filter housing ask him to show and explain to you why uit needs to be replaced, those things are metal and its usally the gasket that needs to be replaced not the housing, the gasket is $5 and the housing is $200 - $300 bucks