Muffler Replace - Eberspaecher?

Based on advice here on a prev thread, I've decided to replace central and rear mufflers. From what I've heard, Eberspaecher is what gets closest to OEM.
I'm planning on doing this on my own. I'd appreciate if anyone can help me with answering the following questions. This is the first time I'm going to tackle this sort of job.

I've had a hard time taking the bolts out at center to front connection. I broke the two shorter bolts and the ends are still fused on to the flange on the cat side. I guess I'll have to spend some more time under the car to get those 2 suckers out of there.

Any trick on separating the two pipes from the cat pipes? They don't want to separate easy. And where are those two seal rings and do I have to first remove them?

Of course I have to order new bolts (2 long 2 short) and nuts(4), also the two seal rings. What about the flange 126 492 02 45 -- can I reuse the old one? it is solid metal but some rust on it. Anything I'm missing?

Do I have to use any sealant /anti-seize at the joints? I think the clamp at the center to rear connection comes with the rear muffler? The rubber hangers are in good shape so I'm planning on leaving them alone.

Thanks guys for any help/tricks/advice...
Cheers!