@Krdax Cho is a solid choice from what I've seen. Great solo top, jungler, had one give me issues at mid before... hell, with this new "everyone can be a support meta" he's probably great in either position on bottom. Having a versatile champ that can play any position and be built damagey or tanky is fantastic to have in your aresenal, specially when you're starting off and really don't want to be switching things up each game more than you have to.
Ever play a FPS? LoL positioning is kinda like Call of Duty where you really only go so far away from your homeys true so you can be protected or at least avenged if you die. Eventually it becomes second nature to keep track of allied firing arcs so you know the safe areas you can turn your back to and not get killed and tbagged by someone who just snuck up behind you. Half an eye on the mini map at all times soldier!
Its not really necessary to mob up at all times after the early game like some folks believe, but how far you stray from your friends depends on a lot of things:
1) Your champs natural escape mechanisms and summoner skills and over all strength.
2) Nearby allies. Are they all on in the general vicinity at least? Remember, its not just a question of whether they can help you but are you close enough to help them as well. Is your closest friend a 0 CS support who'd be crazy to help you if you were jumped or a fed and super farmed Yorick?
3) Location of enemies. Did you just see the icon of the enemy 0 CS support on the other side of the map? Ehhh... oh, they had their fed carry with them? Then you can get a little bolder for a little while.