The access hole also lets you absolutely verify there isnt' any wiring or plumbing in the wall you are drilling into. THAT is priceless if you discover a surprise.
Correct. The rear foam backing of the PFA137 seals it adequately. You can optionally put a bead of caulk around the central hole, but probably not needed. Just completely seal the center hole with duct seal after wiring is all hooked up. That is the last barrier to keep moisture and bugs from entering your wall. Other than that complete seal, think of the rest as things to guide water around what you are attaching to the wall, rather than as a water proof container. Strategy is to make water go around rather than in. Assume caulking failure and think what will happen with moisture that gets in. It must have a way back out. Your siding is built that way. So should your camera installation. That's why good junction boxes have weep holes at their bottom. Those get oriented downward. If the box lacks weep holes, I drill two tiny ones at the lowest location in the box.
Because you have good access from the basement, drilling from below is easier. When you open the interior wall, you will find the vapor barrier right next to the dry wall. Beyond that is the insulation and cavity in which you wish to work. Slit the vapor barrier and insulation with a sharp knife and you can move both out of the way and reach down to your drilled hole.
You already know where things are based on your construction photos, but when unsure, you can drill a diagonally cut piano wire or thin drill bit through the floor next to the baseboard to act as a guide. Find the tip in the basement and you accurately know where you are. A tiny piano wire hole is easy to patch compared to drilling a big hole in the wrong place. I also like to scan the wall with an AM radio to help detect hidden wiring.
Sometimes one is forced to drill downward. This can happen with a 2nd story wall going into a joist space. For drilling down, here are a few tips...
A length of 1 inch PVC pipe can protect insulation from your spinning drill bit. Cut it to match the distance from foot plate to bottom of your access hole. It gets passed through the vapor barrier and placed vertically down through the insulation. Your drill bit goes down through the PVC pipe and remains free of the insulation. No twisty cotton candy effect if you protect the drill bit.
Drilling downward in a wall goes a LOT easier if you get a 90 degree offset drill adapter. A flex bit extension can also work, but is much harder to control accurately. Actually, I love my Bosch right angle drill, but an offset adapter will suffice. Wear gloves and watch out for the bit grabbing and wanting to spin the offset adapter. That can pretty quickly hurt any fingers you have stilling into the hole.
Get drill bits with hex shafts, multiple different length drill extensions (2 inch, 3 inch, and a pair of 5 inch) so you can keep lengthening your drill string but remain in the vertical confines of a rework box sized opening. The short extensions let you drill downward a couple inches and then swap / add extensions. It's super frustrating if you lack the short extensions because you end up stuck between too long vs too short a drill string. With the 2 and 3 inch extensions, you can usually find a combo that lets you engage the offset adapter AND have clearance to drill downward.