Headers VS Manifolds
Header are worth it performance wise,and done right with good gaskets etc they will not leak(very much,lol).I would say that headers should be part of any performance build.Leave manifolds for the cruisers and restoration crowd.
If cost is your objection there are very reasonable headers out there like summit ,hedman etc. Mid grade cost would be hookers.
That being said NO header is easy to install. They will all require some work,like shifting the motor around,dinging tubes,maybe a smaller starter etc.