2. If you mean the rocker arm brackets (the part that forms the upper part of the cam bearings) 21nm, reuse the bolts (PS the front and rear barckets are the only ones that are different (the front has a threaded hole, plus the 2 "prongs" for holding down the front shim. The rear one just has the threaded hole (threaded holes are both for the oil tube, for bolting it down)
3. NO, I'd never replace the chain, not unless you have say several hundred thousand miles on it and intend on driving it several more thousand miles, and you check for stretch and it's stretched more than 5 degrees or so.
If you need to install new valve stem seals, the seals with the dark colored steel rings go on the INTAKE side and the ones with the bright/chromey looking steel rings go on the EXHAUST side.
Soak them in oil prior to installation and use the disposable plastic shields to slide them on the stems to avoid damage from the keeper ribs on the stems. Usually you can do 3 or 4 valve stem seals before you dispose of the shield, MB give you enough to do the job.