.
Your room was
~22 feet long with 8-foot ceiling, wasn't it?
1. Pretty good choice. That wire will be sufficient to drive 4-ohm speakers up to 30 feet, 6-ohm speakers at 45 feet, and 8-ohm speakers up to 60 feet with negligible insertion loss. Although you might consider doing the
4-conductor stuff for future proofing. In case you ever decide to get 4-ohm mains later, the two pairs in 4 conductor wire can be bridged together. And if one of the wires is accidentally cut or some other calamity befalls it, you'll already have spares and won't have to fish new wires. Too much is far better than not enough. You're also going to need more than 100 feet I'm pretty sure, with three runs at least 22 feet plus the height of the wall at either end for your LCR, plus enough slack to handle the wire both now and later. That's not including your surrounds. I'd get the 250-foot spool, and even then you might end up buying more later. Go ahead and pull the trigger on this while it's on sale.
2. Active subwoofers are usually connected via RCA cable. You'll probably want
a couple of these. Unless you plan to build your own subwoofers and keep the amp back in the utility closet, then yes, that speaker wire will work for subwoofers as well. Do you think you might be open to the possibility of building your own subs?
3. No, and you can design your own wall plates using keystone plates and inserts. For example, up front you could install a two-gang, 8-hole plate. Get 3 black and 3 red keystone banana inserts for your LCR, and two RCA inserts for two subwoofers.