550 bar isn't ridiculously high pressure, but a bolted joint will need some serious pre-load to work well.
Materials - should be fairly strong, but not at the expense of toughness; fatigue is always your worst enemy - Low alloy steels are quite common, also some stainless steels. Soluble oil/water makes a good test fluid - it's kind on pump seals, and has anti-corrosion properties (can smell a bit if left to stand and the bug killers get used up).
Clamps or a threaded barrel are common instead of bolts for the closure at higher pressures, also sealing on the bore rather than the end of the chamber will be more forgiving. There are several detail options. An O ring (with suitable back-up ring) can be made to work, there are other options, though more costly.
Fluid connection - stainless capillary tubing is probably simplest at very high pressures, there are compression fittings available, or it can be brazed.
Standard design formlae aren't used at higher pressures - stresses are nothing like uniform through the vessel wall. There are a few design codes that are applicable. Use a minimum design factor of 2 x MAWP, testing should be to roughly 1.5 x MAWP.
May sound 'soft' but you should draw up an inspection schedule for such a chamber as it sounds like it will be pressure cycled regularly. I haven't looked for viewing ports at that pressure for a hwhile, they should be available in saphire.