Tanks are very much needed for every server, many people don't like playing tank or just aren't good enough to.
Yes you can still play on your MA character and change your heroic trait, but you should be alright with your current heroic trait. Heroic traits are nice, but they aren't too much of a game changer, your gear can make up for a bad heroic trait. I have Maverick because it helps every class out, it gives me eva/attack speed on my tank. Gives me attack speed on my melee DPS and RDPS and gives me cast speed on my healers and magic DPS. So I wouldn't worry about it too much unless you've got a magic DPS heroic trait and really don't plan on ever playing MDPS.
What you can expect from a tank class is easy parties, good tanks generally get added to people's friends list and people will beg you to join their party. Of course you can expect a lot of rage if you're not a good tank. People generally blame the tank, even if it's the healer's fault, the DPS's fault, expect to get blamed. Some people will call tanks masochists because of how much punishment they take. Also, don't expect big numbers on the screens, some people enjoy hitting big or healing big, but tanks don't really do that, the most fun I get from a tank is when I outgear a dungeon and just mob up 3 packs of mobs and watch everyone AoE them down.
Also, EE is rather funny with threat/malice, you will find DPS can easily grab aggro, other MMORPGs this doesn't happen that often, but EE is special. Once you get to the higher levels you will find OP DPS that will grab aggro from you instantly and a lot of tanks use DPS gear and a DPS build to keep aggro but try to keep their gear in check with enough defense/eva/block.
Yes you can start tanking early on.
Yes, it's very gear dependent, gears have to spend a lot to keep their gear up to scratch. Also, I find things aren't as straight forward. When I decide what gear I want to use on my mage I go with a few procs, some mcrit there, some mattack there. When I decide what to use on my tank, I have to decide if I have enough def, enough eva, enough malice, enough procs etc. I generally switch my gear around depending on the party. If I have enough malice I'll equip for more defense, if I have enough defense I'll equip for DPS gear. Adaption of gear will change the way you tank.
Tanks are very much needed.
Yes you need quite a bit of money later on.
You can solo, but it's faster to level as a DPS.
Best tanking class is debatable. People have their preferences, but I will say, try them all out and change depending on the situation. Warriors generally have more health, defense and block rate. They also get access to an AoE fear which is a nice panic button, they get a charge with a stun and finally they get an AoE provoke.
Knights on the other hand have more evasion and attack speed, they get access to a triple hit skill an AoE skill which generates quite a bit of malice.
I haven't really touched templar so can't help you there, but think of a magic tank, they are much harder to gear and don't have as much malice on AoE trash packs.
Now it's debatable on which is better, AoE provoke and knight's AoE skill, judgement storm, I'm more partial to judgement storm but a lot of people like AoE provoke. But you will never stick to one tanking class, warriors are immune to fear, knights are immune to sleep, templars are immune to stun. I switch between them depending on what the mobs/boss may throw out. But just try them out and decide which one you like more.
Builds are a bit funny, I would recommend you look at the defensive section in the class information board for that kind of thing.