Currently I am looking at a 10KW solar install. The plan is to install 2 string inverters (5KW ea.) at the house 350ft away from the panels. This would involve 4 DC circuits at about 355V each. Full load current would be about 8 amps. I plan on using 8 runs of 1/0 RW90 cable (4runs x 2 wires/cct) I figure this would be about a 3.5% volt drop. Additionally this would all go in one 4 inch PVC conduit underground. I have never installed DC circuits of this high voltage before, does anyone have any thoughts or considerations on this setup and on working with high voltage DC circuits?

Make very certain that you understand exactly how to wire equipment when using DC. For example; disconnects and safety switches get connected very differently for DC than for AC.

And never forget that there will be DC coming from the panels from the instant that they are taken out of the box. The only way to shut the panels off is to hide them from the sun. Just assume that things are always live and you should be fine.