The answer to most of this is relax, keep your throat muscles loose (yawning actually helps with this). An audience wants you to be good, so they're typically behind you, but if you act nervous, that'll come across in the 'feel' of the gig more than anything.
There's various techniques, keep moving your feet beforehand, to keep blood flowing.
Breathe deep, there's lots of material on this online, but the basic most important thing is to get used to really filling your lungs, which gives you a boost of oxygen and helps keep the nerves away. It's also required to actually sing and produce a reasonable amount of sound. (You do need to project when you sing, the microphone doesn't do it all for you).
Know your material well, make sure you can sing 'in your sleep', without having to refer back to song sheets etc. this takes the pressure off a lot.
Rehearse chatting to an audience, even if it's just a couple of lines that they might respond to. Have a go at "how're y'all doing?", "Are you ready!?!" this kind of statement. or my personal favourite (when having to retune) "I swear it was in tune when I bought it"
How to condition my vocal chords to not be too dry before the gig?
Drink some water, alcohol dries you out, so does coffee. Have some water handy on stage in-case your throat feels dry.
I will be playing drums beforehand, how can I ensure I am not too tired to sing?
I'm not sure I understand this question.
Long term you can work on your physical fitness to improve stamina.
Are you usually out of breath after a couple of songs? If so this may effect your singing, take a break if possible.
When is it too far when trying to have a stage presence? (bare in mind its a heavy concert)
You'll find your feet over time, you need to find out what works for you, but here's some general guidelines.
Match the gig, if there's 4 people sitting at a table, it's not worth trying to play it like you would to a packed festival. If there's a bit of a crush standing at the front, I'd say go for it, you can't be too big if there's a crowd who'll go along with it. Guage the situation you're in.
Don't actually insult your audience, or the promoters, sound tech, bar staff etc. This will not end well.
How much should I engage the crowd?
Play well, talk a little. But most importantly try to enjoy it the way they're enjoying it. You're a part of the same scene they are, after all.
