I will be changing the valve seals, but should I also change the valve guides?
Only if they showing wear or you have the cash and plan to keep the motor a while.
I plan on polishing the exhaust valves, but should I polish the intake valves as well or will I be better off leaving those with slight pits or dimples.
The valves can be smooth but I wouldn't polish the intake valves as that can encourage fuel to pool.
In this case, should I also polish the intake manifold or will it be better to leave it as is..
Port match, no polish... some turbulence can be helpful on the intake side.
This is my first time porting a head and I will appreciate all the help I can get including suggestions as to which machine shop to use etc
Unless you particularly want to learn to port, it's best to leave port work to a more skilled person. I always tell people that a good radius valve job is a great benefit... port match the manifold and replace seals as necessary and it would be a decent job. Other than that, a little port and splitter work with a bit of polishing on the exhaust would be nice... you can do it yourself, but it's easy to screw it up.