Yes Ultimo. I use the move speed quintessences and utility masteries to maximize my speed too.
Lingie#3148 on Discord. Lingie, the Fox-Tailed on Steam.
I actually got Kennen with RP, he's one of the very few. I decided to say hell with it, got lazy, and spent a few bucks on him. I'll use what extra RP I get on a skin if I find one I like.
None.
It might be a timer based on when you killed it, but I'm not sure. I don't remember ever seeing all of them respawn at once. I think I've always seen them respawn in about the order they were killed (excluding ones that take longer).
None.
Each one has its own respawn timer.
As for buying heroes, every few weeks I buy RP and get a couple new heroes I like or want to try. Today I bought Miss Fortune, Pantheon, and Ashe. Miss Fortune is crazy fun to play. Pantheon is great, but I'm still trying to get the hang of it. My endgame with him is better than my early game. That goes for Ashe, too, though I'm mainly having an issue with staying ranged with her since I usually play melee characters (or casters in melee range, like Heimer).
Currently Working On:
Myself
Noooo, they made it so that you need two players for practice games. Now I HAVE to play with you guys

They've been changing it around all the time. Sometimes you can play by yourself, sometimes you need one other person, sometimes you need at least 3 other people.
It changes based on server load. More people playing = more players needed, so that practice games are making the servers run slow. Basically encourages people to play real games if the servers are under a heavy load
Who's the best tank for a good price? Rammus or Cho'gath, I don't mind either gameplay, but I think I prefer Rammus to be honest. 
EDIT: Does Boots of Mobility stack with Rammus rolling skill? Because if so, such imba speed then!
Rammus is the better "tank" by definition, and can push pretty hard. Cho'gath is better at soaking up damage, and doing decent damage.
None.
Did you buy Ashe with IP or RP?
I haven't bought any with RP so far, only IP. All the 450's, one 1350, two 3150's, and one 6300. Miss Fortune is the one 6300 I have - at the latest, I started saving after I saw her skill list in the patch notes.
None.
Yeah, I did a few practice games with her and she's awesome if she can stay away from enemies. Her one drawback is her low health, but the MF we played earlier was smart enough to stand way in the back in team fights.
Master Yi is slowly becoming my favorite champ. I'm not sure about jungling him, but he does pack a massive punch.
EDIT:
I bought Ashe with IP, though I have 1000 RP left and I need IP for runes. Oh well.
Currently Working On:
Myself
Recently I've been trying a build focused on raw damage points and life steal.

This gives her ult high damage and heals you significantly when you fire Double Up, besides how much regular shots give you from it. Surprisingly, the build doesn't particularly seem to need any attack speed bonuses other than her active ability in most cases. It also gives pretty good survivability as long as they don't burst you down or prevent you from attacking.
I once had a little over 100% life steal in a long game when using this kind of build and I was very hard to take down when none of their CC champs were around, similar to how a DPS Sion can tank with his ult under such circumstances, except it wasn't a temporary life steal buff.

Also, I've had fun catching people off guard using Impure Shots with this build and preventing them from stealing as much life back as me, even Warwick.
None.
Noooo, they made it so that you need two players for practice games. Now I HAVE to play with you guys

They've been changing it around all the time. Sometimes you can play by yourself, sometimes you need one other person, sometimes you need at least 3 other people.
It changes based on server load. More people playing = more players needed, so that practice games are making the servers run slow. Basically encourages people to play real games if the servers are under a heavy load
Who's the best tank for a good price? Rammus or Cho'gath, I don't mind either gameplay, but I think I prefer Rammus to be honest. 
EDIT: Does Boots of Mobility stack with Rammus rolling skill? Because if so, such imba speed then!
Rammus is the better "tank" by definition, and can push pretty hard. Cho'gath is better at soaking up damage, and doing decent damage.
Whats great is how both can be extremly damage intensive, depending on your score or laning.
Theres nothin' like rollin' in to someone unexpecting, taunting them and holding them with Defensive Ball Curl and Thornmail on. Delicious kills.
Lingie#3148 on Discord. Lingie, the Fox-Tailed on Steam.
I learned yesterday that sona isnt all that great by herself
None.
I learned yesterday that sona isnt all that great by herself

Unfortunately no. She can make a mediocre team win, but she can't carry a bad team. Although, with enough AP, she can usually kite just about any non tank and kill them, oddly enough.
None.
Sona is a major ass-pain. She can support the hell out of anyone, better than Soraka. And she's also got a pretty strong damaging ability.
None.
I saw an AP chogath who did pretty well. 1:1 AP ratio on his aoe spell. Pretty good for team fights, it forces enemies to spread out to avoid your stun, or they just get stunned and take a ton of damage. The best part is that AP chogath can still tank as well.
None.
My personal favorite: AD Ezreal.
Manamune - Boots of attack speed - sheen - black creaver - frost hammer - infinity edge
Manamune gives you enough mana to be able to spam your abilities, and also insane attack damage late game. Your Q spell, which you should be relying on, is proc'd by sheen so that increases your damage out put very much. It also applies black creaver which increases your damage and actually lets your melee hits do pretty good damage too. Frost hammer for survialbility and it makes it easier to chase and hit them with you Q more times. Infinity edge just for the damage and luck critical hits.
Or
this which seems to be a popular build, but I find it not as nice.
None.