The biggest problem with parallel banks is keeping all the batteries equally charged. Even very short runs of large wire still have a bit of resistance. So, if you just lay all the batteries side by side and use jumpers down the entire length, then pull power off one end, the battery at the end you are pulling from sees less wire between it and the load than the one at the other end of the string. Same thing for charging, it's easier to push power into the closest one than the one at the far end.
One option to overcome that is to tap power at diagonally opposite ends of the bank, so if you are standing at one end of the string you hook (say) the negative there then the positive connects to the battery down at the farthest end. That puts the same number of "links between batteries" in the path current takes through any battery in the string. (This is what I have done with my 12V bank.)
On the charging, the "recommended" charge rates are generally in the 5-10% of total AH capacity range. Some AGMs actually go much higher. Your batteries are 100AH capacity, when you parallel them you wind up with 1400AH. 5-10% of that is 70-140, so the recommended charge rate would be 70-140 amps. Personally, I've found it isn't always necessary, I have successfully kept batteries charged with 2-3% of AH, but it's slow and (with solar) very likely to mean many frequent days without full charge if the day isn't bright and sunny, especially if you use very much of the bank's capacity at all.
Here's a website I found quite useful for learning about batteries and charging, it'll tell you more than you ever wanted to know about them! :-)
http://www.batteryuniversity.com/index.htm
If you have a real reason / desire to run 12V, there's certainly nothing wrong with that. My bank is set up 12V, but that was because I run my ham radio gear straight off of it. And as others said, it's a lot easier to find 12V "stuff" to run straight off the bank. But if someone isn't intending to get 12V gear, and their primary interest is items that are going to run from an inverter (as your list suggested to me) there's no real need to do so.
The higher you go with the voltage of the bank, the lower the current. That is really the whole reason in a nutshell. Current flow is what generates heat and losses, and requires larger / lossier / more power hungry devices to handle. So the lower you can get it, the more efficient everything will be. It can also be harder (or more expensive) to find switches, breakers and such to handle the larger currents.
The most interesting thing I have found is how hard it is to keep the voltage drop in a run of wire acceptable. Most of the wire sizing charts you will find are based on an "acceptable" voltage drop. That is, if you run up to the amperage limits they allow, you WILL have X% voltage drop. At 120V, that might be okay. At 48V even, it's not too terrible. But at 12V, with so little room between full charge and discharged, it can be a real problem for some electronics that are sensitive to it.
And while yes, 48V is potent, I would say a 12V bank has the potential to be just as hazardous. It needs to be well-protected from prying fingers and eyes regardless of the voltage. A metal tool (or anything conductive) accidentally dropped across a bank with that capacity is going to vaporize metal, sending what's left flying in a big bang. You won't have the big problem with hydrogen gas generation that a flooded-cell bank would, but even AGMs can vent gas if overcharged.
Anyway, as you said initially there's plenty to learn so jump in and have fun! :-) There's no reason you can't decide later to rearrange things if you want. I have already done that a couple times myself. I've only been reading about and experimenting with this stuff for a year now, started with the Harbor Freight 45W kit last summer and just finished a 500W system this month. I did have a little head start, as I'm an electrical engineering grad but the whole off-grid power system idea has been a fun new learning experience for me.
