I won't comment on Bard or Kayle bot lane play because I don't play them frequently enough. As for the unicorn, I do the same thing and the ADC in most cases ends up pushing the lane hard (and if the enemy ADC is any good at farming under a tower it does me no real good to get him to a point where he's afraid to farm, but we're giving him a safe zone to do so). You have no real control over where the lane is unless you want it pushed in which case you can force it, but leaving it up to an ADC generally means you'll be sitting at their tower. Best thing you can do is ward the river, and every time your trinket ward goes down ping and ask for a ward there.
As for not running out of mana while poking, as Raka I have Mp5 Quints and Hp5 Seals for sustain, I've been starting with Crystalline Flask and generally one mana potion and the rest health, and I start and max Q first (Q->W->Q->E->Q->R unless the enemy lane an all in that has been landing hooks before level 3, then I get E at 3 to help mediate this). Leveling Q first gives Soraka a nice amount of damage especially if you can hit the center frequently, but even then hitting the enemy ADC with a Q and an auto is painful enough. I alternate auto attacks on the ADC and support to get pick pocket procs off both as often as possible while maintaining position to not be dove. Getting heal at level 2 gives you a the heal on Q, letting you sustain any poke your ADC gets, too much poke is offset by crystaline flask giving you both mana and health back, otherwise I have my runes set in place to regen and light trades without the use of potions. I try to time Qs for when the enemy ADC moves forward to last hit, generally hit about 2/3s of the time unless I'm trying to hit both targets and fail.
Depending on how the game is going I'll switch over to leveling W after 6, but for me at least, this set up works well. Even if I spam Q, I can generally last until level 4 at least before going OOM, if I'm timing it to the enemy ADCs last hits I don't run out of mana ever. Crystaline flask also lets me recover very easily from an all in on myself or my ADC after level 2 because it pretty much let's me reset my side of the lane in terms of health levels.
Hope this helps.