A spa has no need for clarifier. If your water won't clear from a shock it's time to drain and fill.
Stain and scale is generally uneeded unless you allow your ph and alk to go too high. Some water with alot of metals needs it, but most municipal water system users do not if they keep it balanced.
I am not a fan of mps (non-chlorine shock). It is guesswork how much to use and it throws off your chemical test readings when present in the water as a residual, leading to other issues. I will use it if I need a shock but don't have time to allow fc to drop before use.
No, a little in the pipes is of no concern for bromine. But as mentioned, with Ahh-Some you will have to do a rinse as well. You may also need to use the Ahh-Some more than once to eliminate all the biofilm.
???? Built in tablet feeder?

How old is this spa?
Technically, yes you need to replace the feeder, but only if you plan on destroying your spa by using tablets. Read the sticky thread on dichlor/bleach method in the chemistry section. Please.
Do you have ozone?
A SWG shocks for you, in a sense, just as ozone and uv. If you do not use any of these you will need to shock, but you can do so accurately with chlorine by raising fc to 10 times the cc. If done frequently it will not be an issue, but if you have to raise fc to 20 to burn off 2ppm of cc you will obviously not be using it for a bit, so might want to use mps instead.