Our shop does them quite often. Many times we have to take them apart--and sometimes we get them already un-assembled. Yes all seals need to be out of them. As RPM said, take some time with a grinder and flap wheel, or a right angle die grinder and ro-locs and get them smooth. It'll make them look tons better.
As for taping and plugging, a good shop knows what surfaces to take and what holes/threads to plug, but it doesn't hurt to tell them. Here is a pic of some GM calipers we did.