Answer me this: When should a player start considering what character to be good at?

I'm nearing about 200 games, and about 300+ hours spent on DOTA 2. I realized that although I could pick "Random" for every All Pick game I play for the rest of my life, but I feel like if I ever wanted to play cooperatively with people, I'd have to pick a few characters to be good at. Also, there are obviously people out there (including the ones playing high ranked tournaments) that practice with just one, if not a select few, of characters in order to be more effective than well rounded.
So, when would be a good time to start doing that or how would i go about choosing which characters to master? I'd assume I'd need to master a ranged carry, melee carry, ranged support, melee support, and a tank, correct?

That's a good idea, being a master at every role, but first you should find a role that you like, such as support, roamer, nuker, etc. for me, I personally like nukers, but I know how to play carries and others.

What Glayde said, it's good to play every role, so you know what they can do, what they must do, what's their weak part, how to counter them and so on.

Master the role you like the most, the more you like it, the better you play it.

Good luck.

According to DOTA 2, Lich seems to be my best character, but I enjoy playing a good Juggernaut the most. The problem is that I haven't really found my niche yet, but I like doing high ranged DPS just like every other guy.

I also hate being called a noob because the characters I play (that I'm actually good at) are easy, and also I hate being called a noob for playing 1 character over and over again.

Ignore other players, just play, have fun, and enjoy the game!

Also, try making friends to play with, so no one will ever call you a noob.

All my friends in RL complain that DOTA 2 is too hard and they stick with LoL because it's easier and "more fun" to play.

They must be 12 years old or DotA 2 is too hard for them.

If they jump off a bridge, don't jump too, be better than them :) Don't give up pal.

Thanks, I'll do my best. I played LoL just to humor them, but it was too easy, and I hated the "pay 2 win" system.

It's not necessarily a pat to win, but I understand what you mean. Keep trying, and is you like Lich, right? How about try other supports, maybe give Lion a try? And as for Juggernaut...maybe Ursa?

I like being able to kill the enemy fast and efficiently, and being useful in team fights. I find Lion is extremely easy to counter if the other team has a Morphling, and I like Jugg because I can be in and out. I'm bad when I dedicate myself to a straight up melee fight cuz i get too distracted and end up not firing off skills or items.