A few tank busting questions

[War Barney]

Hi, basically I've decided my goal in planetside is to blow up tanks by sneaking up on them and throwing C4 at them. As such I have a few questions to ask to improve how I do this.

First off should I just save up for a second C4 right away or is it to expensive for what else I could get with the certs?

Second, whats a good rocket launcher to use? I'm NC and was going to get the decimator but people keep saying the phoenix does the same damage but you can camera target it. If my style ends up with me right behind the vehicle I'm trying to blow up most of the time which should I get?

Third, are the anti vehicle grenade useful? all I've heard of them is that they do hardly any extra damage compared to normal grenades so its not worth getting them.

Fourth, (a bit off topic) is how worth it is it to get the second grip upgrade for the starter lmg? I was going to buy a new gun but I've found I get a nice amount of kills with this one and like how it seems to work at all ranges, got the compensator and first grip so far so was wondering if I should get the next one. Also while on this topic is there a good thats a better all round gun? I heard the GD22S was good for this but is it really worth buying over the starter gun when I have so many upgrades for it already? Also is the high velocity ammo worth getting for this gun considering I try my best to get close up BUT do tend to notice a lot of long to mid range combat does occur thus why I don't really want to switch it for a short range one like I was thinking before.

Sorry for the semi wall of text, been playing about a week and decided its time to start planning for the future with certs and guns so thought best way to get somewhere would be to ask people who know whats going on as right now I'm very confused =( guns seem to say they are anti vehicle but the damage says its lower. Why can't they just have a damage vs vehicles and a damage vs infantry stat! would make life so much simpler.