I noticed that the price for the German produced version increases with each right-sided option selected. This implies that the Magnum has the highest capability, probably a good idea considering your high temperature objectives. The same suggestion applies to the power supply choice. More power is always a good idea when it comes to heat. Additionally, if the Magnum is selected, the Bondtech extruder becomes mandatory, and it's a good drive system. I have two of them on my Sigma printer and they are great.

Consider also if you are selecting the 420 size option you'll want the larger diameter rod selection to provide the additional stiffness for such a large assembly.

Textured PEI means a fine irregular surface on the bottom of your prints, like fine sandpaper, while smooth PEI would give you fairly smooth surfaces. It's a matter of personal preference. I've seen a few Prusa home-made enclosures that appear to work well, so you should be fine in that respect.