Direction of tap out of water heater
I'd strongly suggest that you ask the &quot;why&quot; questions to whoever it was that made these recommendations to you. That person may well know your local codes and/or the particular unit you're planning on installing better than any of us will. That said...

Generally, I believe your &quot;security group&quot; is called a &quot;pressure relief valve&quot; - it opens automatically if pressure gets too high, and drains the water someplace, hopefully where it's designed to go (like a drain). I'm not sure, however, what this has to do with your question at all.
The item in your 2nd image looks like it's got a garden hose thread on it. Beyond that, I can't imagine why it matters whether it's a straight or angled fitting beyond the fact that the angled fitting will more easily allow you to turn the outbound plumbing along the wall, which is where you probably want it. If you need the plumbing to go straight out from the tank, I'm sure you could use a straight fitting here.
Having a valve right at the outlet from the heater allows you to shut off water flow to the entire house if necessary for plumbing repairs, preventing pipe freezing in case of power loss in freezing temperatures, etc.
Generally, the outlet of the valve points in the direction the next section of plumbing needs to go. If you need to run up from your outlet, point the valve up; if down, point it down; likewise for left or right.
I wouldn't see any issue with installing a pressure gauge right off the hot water heater. Make sure that the gauge you pick will support the temperature of water coming out of your heater. I would install a valve before the gauge, though, just in case the gauge fails &amp; needs to be replaced. The valve is a handy shut off to keep your floors mostly dry while removing/replacing the gauge.
Again, confirm all this with your local building/plumbing inspector to ensure that it meets all applicable local codes.