I'll try to give you answers.
1) yes it should be fine, just keep in mind that all gear has limitations.
2) I'm not sure why you're tying mono to mono, and using braid too, but the Spider Hitch is a good knot and should be close to 100% breaking strength if tied correctly. Most folks who use braid, add a length of leader, so one knot to connect the two lines, and another knot on the terminal end of the leader. Folks have different thoughts & reasons about using leaders. Generally, they're for abrasion resistance when using braided lines. Most folks don't use an extra shock leader too unless fishing for specific types of fish. Tarpon are a good example where a shock leader might be used.
3) Here again, hook sizes can vary, but a good size 2 or 1 is fine for puppy drum. You can go up in size for targeting larger Drum, and that might depend on the type of hook you choose. Live Bait hooks are usually stouter wire than an Octopus for example. Circle hooks are a good choice for using baits, but sizing with them is not going to be the same as sizing on other styles. Sizing is not standard either between different hook makers, so use a size that fits the bait & the fish. For drum, probably hooks in the 2 to 3/0 range for "J" hooks should work fine.
4), this too varies with what folks like to use. 80 lb is pretty stout, and possibly a good choice as a shock leader if fishing around rocks, or a lot of oyster beds or barnacles. Many folks prefer fluorocarbon now for better abrasion resistance. 30, 40, 50 lb can be fine for some fishing and easier to tie knots. There's no single answer to this question.
5), snell knots work well with hooks that have up or down type eyes, not as well on some hooks that have straight eyes. A straight eye hook that has a larger eye can work fine with a snell knot. Again, depends on the hook. Generally a snell knot is a good choice. I've known guides who snelled leaders to Tarpon flies, which are tied on straight eye hooks. Here again, there's more than one type of knot that can be used for attaching leaders to hooks. The snell can be a good choice.
The fact is, you may have to experiment some to figure out what you like to use and what will work best for you. There are no single answers to any of this.
In the past, when I was a kid, I caught puppy drum in the Inland Waterway on shrimp baits, using an old spinning outfit and 10 lb line. I used a single hook above a 1 ounce sinker and the hook was tied to a dropper with a Palomar knot. Nothing fancy, and this rig has worked fine for other fish too, but it worked well for where I was fishing and the fish size I would most likely to catch.
No matter what you use, it's all a compromise. If you hook into a big Shark for example while fishing for those Bull Drum, it may or may not work well. In saltwater. most folks rig up for what's most likely and what they' want to target.
Always have extra line & terminal tackle, and not a bad idea to have extra rigs ready. because you'll likely lose some eventually.