junction between PV cables and THWN in conduit

20200512_121245.jpg This works. You can get boxes of any size at a home center or hardware store. This is a 4 X 4 and deep. Note the label. I drilled the holes for the conduit, the glands and ground. I know they make models in 8 X 8 and 12 X 12. I think the manufacturer is Carlon.
Inside I use a silicon filled connector called a Tap Conn. I found it at a home center and it floats inside. I am trrying to find a phote. It was about $3.00 Note the glands on the solar panel cable and they loop down then up for a drip loop. The copper ground is barely visible and doesn't use a gland because the hole at the bottom provides a way for moisture to escape. No matter how waterproof they are water can enter just through moisture in the air and condense.

So many questions, I've searched but no definitive answers ...

In my ground-mount, I'm trying to figure out the transition from the MC4-connector cables on the panels (which I'll connect into two strings) to the THWN conductors which will run in buried conduit to where the string inverter is located on the side of the house (near the load center). The conduit run will consist of a 10awg ground, and two DC pairs in either 10awg or 12awg. I've already buried an "L" of 1-1/4" PVC conduit in one of the footing/piers for my system (so it sticks up vertically beside one of the 6x6 posts, and emerges from the side of the pier at the 18" depth required for the conduit run).

Clearly I need some sort of waterproof junction box, at least 9*2.5 = 22.5 cu-in (but hopefully a bit larger). I doubt I'll find one with a 1-1/4" opening (dunno if it's called "knockout" in a PVC box) that's not enormous and expensive, so I'll have to reduce that vertical PVC from 1-1/4" to 3/4". It also needs openings for the various wires that enter it, the 4 conductors for the two strings, and ground. I believe these openings require things called "glands" to seal where they enter the box. Is it one gland per conductor, so 4 for the DC pairs, and one for ground if it runs inside the conduit ?

I'm unclear on the ground. I'll have bare solid 6awg running between clamps on the IronRidge rails and to a ground rod. Somehow I need to connect the conduit ground wire to this system. My inclination is to make the 10awg conduit ground wire be stranded and insulated and run inside the conduit; is this correct ?

Sounds like for making the connections, wire nuts are considered to be questionable, unless they're the silicon-filled type. Maybe terminal strips are better ? If so, how to mount in the box, or just floating in there ?

I'd appreciate comments on whether I have all this right, and pointers for buying the junction box, glands, connectors.