not to be negative but.....
well for 2, all supports should buy wards, and all supports have abilities that they need to use properly (soraka silencing, sona harassing, ali headbutt/knockup)
for 3 this also applies to all supports (when ali goes in for a knockup+headbutt, or when taric goes for his stun, or when janna knockups you have to be ready)
for 4 this also applies to all supports.
The real trick to blitz is #1. its his grab that makes him what he is. the better you get at grabbing THE RIGHT target, the better blitz you are.
some pointers are
1) not grab until after you powerfist, or until after they burn their escape (flash, rocket jump, etc) you basically wait in a bush for someone to get close or past you, you hit w for speed boost and run towards them. he will either get knocked up or use some escape in which you grab to pull him back into range.
2) grab through walls. (wards help a lot for this). his grab has fairly long range and can hit people through walls.
3) some people should not be grabbed. just because they are in range doesn;t mean its a good idea to grab them. take kennen for example, its a team fight and you grab kennen....you guys are probally all grouped up so he'll ult and hit everyone. you basically did him a favor.
another example is early game and your against a leona+anyone else. if you grab leona you basically just pulled her closer to your adc so she can own him with her retarded amount of stuns.
like Trolosaurus said the proper target means everything.
4) just like any other skillshot, lead the grab. if someone is moving left, aim it a little in front of them. this seems like a no brainer but i feel i have to mention this.
5) ward bushes. everyone walks through bushes and sometimes hides in them waiting for a gank so its a perfect time to grab them.
6) and the most important piece of advice.....people will get pissed at you for missing grabs. its always the noob blitz fault for losing the lane because he "can't land a grab". blitz is the easiest support to blame because his grab has such a huge payoff and if you can't land grabs you have no other supporting abilities. IGNORE THEM. keep playing to get better, if you have a bad game no worries, and just keep practing.