"2) Have a champ that can defend against Promotes or clear minion waves very quickly, in a way that the enemy promote will pretty much have no effect in you or your point. Im guessing Morgana/Soraka could do this but Im just guessing, I havent seen anyone really do this effectively."
I play Soraka exclusively in this game, and I run her bottom every game (including when we get a Heimer that wants bottom. I'll ask him to go top while I hold bottom, and it usually works out incredibly well because once we cap top, they can't push past him, or me at the bottom, so we have 3 people on map control / gank patrol mode). I wouldn't say that she's good at dealing with the promoted minion (they just have so much health and take forever to kill), but she nukes minion waves fast, and she slowly whittles that thing's HP down so it wont get to your tower.
I like to run her with Promote (and so far I'm using Flash, but I'll probably change it when it gets rebalanced). The strategy that you mentioned is exactly what I play to do - force them to send extra guys bottom so we win in the 4v3 on the rest of the match. Unfortunately I still lose matches like this because I'm holding bottom 2v1 all game long and then I look up at the score counter and we're behind by 200 since my team doesn't seem to know how to do anything.
When it does work, I have games where we're 400 to 100 ten minutes in.
I'll agree that counter-building is crucial. I build the same core every match (Mercs + Frozen Heart + Abyssal Scepter), and then very the last 3 items depending on the enemy team and their gear composition. I try to build tanky, but sometimes if I'm against the right enemy composition, I can build super aggressive to match my aggressive playstyle.
Anyway, for people that are wondering, aggro Soraka soloing bottom with promote works sort of like this:
1. Unless you're against Heimerdinger or someone that can effectively outzone you consistently, push up their nose at the start, maybe getting the kill. I open with 2 points in Starcall and 1 in her Silence move. When I get to the middle of bottom, I'll put my 2nd point in Silence, and try to open with that because of the range. Then I chip with Starcall and get the HP shrine for the health restore (since I know I'll get hit once or twice) and the mana (way more important so I can keep spamming starcall). Promote, and just nuke their minion waves as you slowly push in. By the time you push all the way to their point, they either die or run, you cap it, then retreat for gear + healing (this is where I need to use your hiding places to keep them from knowing if I ran or not, and then walk back the long way so they don't see me coming).
What's effective here is that if you have to focus on the 1v1 bottom, or even maybe a 2v1 bottom, your minion wave with the promoted minion will negate their point for you and even the fight. Sometimes they'll even capture the tower for you! This is key for my strategy. You don't get points for this (at least I haven't noticed getting any points), but it's crucial for stripping away any advantage over you that they have.
2. Once you have that core build going, you're the aggro tank. Vs tanky characters, you try to "out-tank" them. Starcall goes off every 2.5 seconds, and each one drops their MR by quite a bit, so after about 10 seconds, their MR is like -48 from your attacks, and another -20 from your staff. At this point you're actually hurting them if you weren't before. If after all of this they run away, you just stalled for time if nothing else - remember that you have more staying power in lanes, and while they're running off to heal, you self heal, grab a health pack, and you're ready to push their lane or deal with someone else they sent bottom to hold for time against you.
If it's a high damage squishy, their MR is almost negative just from walking up, and it will be after 1 or 2 Starcalls. Lead with your silence so you get to hit with Starcall once for free, and their HP will probably be like 2/3 at this point. Try to survive to land 1 more silence (you'll get off 2-3 Starcalls total in this time, so it'll do full damage or EXTRA damage), and now they're almost dead.
You farm fast because you get minion kills. You can hold against a large variety of characters (some will hard counter you, and some will build hard to counter you, going all MR while just having better HP and damage output, but for the most part you can hold and push against plenty of characters). You nuke their high-damage characters (though you'll be low on hp immediately after). Your Starcall acts as a detector for their invisible units (I had a match with Twitch and Eve on the enemy team and shut both down, even killing Twitch while he was still stealthed and trying to sneak up on me).
I'm not an amazing player and I don't care to be. That said, I've been told "This match was 5vSoraka". She's really powerful bottom and while she can easily be countered, they have to build to counter you, and your team can easily build to counter them. Spam that promote and constantly push their lanes. If your minions are capping points, you're not getting credit, but you're doing your job.
Don't play to win. Play to make the other team lose.
One more thing I forgot. If you're absolutely screwed and have to go 3v1 defending a point, just ****ing do it. Starcall interrupts whichever of their guys is capping the turret, so they can't keep it from firing. You can Silence one of their guys and shut him down. Just walk around and try to dodge as much as you can (preferably silencing the one that has the fear or silence or stun - ignore any immobilizes). You wont keep them from capping the point, but you'll take at least one of them with you and make it easier for your team!