League of Legends (LoL) Question: Making a team comp for my ranked team, help me out a little? <3

A tip: don't go all around trying to change the meta. Stick to the current meta for better results. Regarding teamcomps; it really depends on what champs you play. There are global setups (involving Nocturne, Twisted Fate, Shen, etc.), AoE setups such as Amumu + Anivia + Sona, Assassin (ST) setups that revolve around taking out a single target (e.g. Kassadin + Shaco).

Anyway, regarding your original question. I found that Cassiopeia/ Soraka has some nice potential in bot lane and that Vayne and Draven do well in top lane.

Well, if you want to abuse an Amumu passive, then have an AP top and AP mid. Then you'll have 3 AP-oriented champions (4 if you include most support champs).

AP Tops: Vladimir, Rumble, Katarina, Nasus (in a way), Teemo, Warwick, Mordekaiser, Elise, Singed, Jax (though he's technically hybrid), Kayle (depending on how you build her), Nautilus... amongst others.

No need to consider an AP bot-lane.

But, I do say this: Do what works. In tournament play, they change things up a lot, to tip the advantage in their favour. You might do a duo mid, for example, and try and snowball that lane early, before switching to a roaming strategy, etc etc.

If playing an APC bot-lane lets you snowball well, then go do it.

For ADCs that can go top-lane:

Vayne (true damage is a good counter to some solotops), possibly Corki (not sure if he's viable there anymore) and Kayle are all I can think of.

I can't really help you with this, certain team compositions are better than others, and some team compositions are definitely harder to play than others.

If I play with my friends, we will always try to go with a composition that will counter the opposition's one. If we can predict it.
Although it's not for everyone, I find it to be much more useful.

General comps I think that are conventional and easy to play are:
Poke comp(AP nid mid, Jayce top etc, basically any champ with sustained poke)
AOE CC(Curse of the Sad Bullet time(Amumu MF combo), Galio, Kennen, Morgana etc, any champion with heavy CC that can hit multiple targets)
Anti-AOE CC comp(GG Renekton Xinzhao wombo combo etc)
Single-target team(Assasin-mainly team or team with heavy single target CC, who aims to kill one guy then force a fight)
Bruiser comp(If your team is relatively new, this means that almost all of your team members have the ability to go all in and dive)
Global pressure comp (Imagine have 2 TPs or Shen and TF in the same team)

Harder comps which are situational:
SHIELD COMP
Early game shutdown comp(Urgot, Draven, aggressive ADcs and strong earlygame junglers)
Disengage comp(From experience, VERY VERY hard, perhaps the hardest to pull out, but heavily counters a teamfight-oriented team)

Basically I'm giving you all this to consider in team select and talk about it with your team.
If you need more info on any of the comps you can PM me (though I doubt it lol).
And in response to your question I don't really find it viable UNLESS your top doesn't get killed/bullied early and APC bot can get kills.
And if you want to run APC bot you better get a lane bully such as Cassiopeia and Orianna.
Though I don't really think your comp will work cause sending an ADC top is generally a huge risk as if he gets shutdown you have no lategame power.

try not to think of a team comp beforehand, because you want to be counterpicking the enemies picks. Jungle amumu can be countered pretty hard, it isn't that consistent. (if the enemy can just take maokai, shaco, shyvana, mundo)