It is indeed confusing at first. You just need to get used to the terminology. Here's a quick summary:
First, there are two sizes of cables
and connectors; Mini (bigger) and Micro (smaller)
Mini (bigger) is used exclusively to build larger, longer backbones. For a boat under50' or so it's unlikely that you will need to use a Mini backbone, but can instead use Micro size parts
Micro (smaller) cables
and connectors are universally used to connect to devices. I don't think devices ever have Mini connectors on them. My boat is 47' and has a N2K backbone that runs from the top of the mast
to the very stern with 20+ devices on it, and it is built entirely out of Micro cables and connectors.
The only thing that will drive you to build a backbone out of the larger Mini components is if your network ends up with too many devices and/or too much length. Since power gets distributed to the devices by the network, there is a voltage drop every foot, and every device. There are limits on how much drop is allowed before things stop working reliably. The larger Mini cables have fatter wires and can carry more power, hence are called for in bigger networks.
I think the best way to sort this out is to use Maretron's N2KBuilder program. It's a free download (you might have to register first), and let's you "build" the network on paper and check to be sure you are within spec on everything. If you have a problem, it will tell you. I'd assume you are building everything out of the smaller Micro parts
unless N2KBuilder tells you it's not possible.
You are correct that devices are attached to the backbone by inserting "T" connectors, then running a "drop" cable from the T to the device. The drop cables are always Micro cables, and the very same cables you will use for your Micro backbone as well.
"Mid taps" are all about how you supply power to the network. Ideally, you want to locate the power tap near the middle of the backbone. That way the longest distance to a device, and hence the largest possible power drop, is half the length of the backbone. In contrast, if you put the power tap at one end, then the longest distance is the full length of the backbone and you are twice as likely to have unacceptable power losses.
Building your network with N2KBuilder can be a bit tedious, but it's worth the time. Not only will it give you a network that you can be confident in, but it also serves as a great way to document it for future reference.
As for parts, the Maretron stuff is very high quality, but expensive. If you shop around, I have found the Garmin
cables and Ts to be more affordable, however the fittings are plastic as compared to metal on Maretron. Actually, in either case shopping
Once you get comfortable with all this, then we can talk about how you can tie your N2K bus to the various proprietary variants like Simnet and SeaTalkNG. The good news it that it's just a matter of connectors and cables.