Oh man, I've been there, what a tough break. Those things can really seize in there. I would spray the collar with a penetrating oil, it seems traces of oil can get in there and turn into varnish, which can be softened with penetrant and maybe some taps with a hammer and small punch. Then to have something to pull on it with, use your best judgement. I've used a hole drilled into the front with an "easy-out" threaded into it, then pull on the easy out. If you soften up the varnish as I described it shouldn't take too much to get it started. Once it's drawn out 1/4 inch or sor you should be able to rotate it in the cam, which will help break up the varnish and make it easier to remove. Don't try to rotate it while fully in the cam as it is indexed to the cam. Best of luck, this can be tough, if it's getting difficult to deal with spray more penetrant on it and take a break!
Before disassembly you can check for chain stretch, there is a spec for the allowable degrees the chain can stretch. this is the only accurate way to tell if it needs replacement or not. Many will suggest doing it as a matter of course.
On the belt, is it off already? The best "easy way" to tell if the tightener is shot is to look at the threaded rod inside the adjustment nut (with the belt installed and tightened). If the threaded rod is way down at the bottom of the hollow nut, it's probably worn out. Only way to know for sure is to remove and inspect the tightener. The 2 "flats" on the inner section where the adjuster connects should line up with the tensioner pulley. If it's off by I believe 10 degrees, it's worn out.
Also on the small gas strut on the tensioner, if you can push either one of the aluminum inserts out of the mounting eye (what the bolts go through) you should replace the gas shock as well.