To the op, the answer to all your questions is DON'T start a mage. Seriously, it's not worth it. I'm not even going to go into the drama or complaints. Start a mage and I can guarentee that you will be miserable starting at level 125ish and definitely at 180ish unless you have godly amounts of sigils (both hp and energy). You have been warned.
Would 500 sigils split between hp and energy be enough?
The thing is, I have had a warrior and I got bored because of numerous reasons. I already have a decent level druid and tone plan on going all the way. My brother has a rogue which is amazing, and to have a repeat is useless. That leaves me with mages and rangers, and I personally think mages are a better class, provided they have sigils.
Hi, I honestly can't really remember for all levels but I can tell you that at 180, you need at least 1.5k energy sigils if you want to have spare points not used in energy boost.
To solo, you would need around 500-1k hp sigils while using freeze. I would go something along the lines of attack a mob, wait till hp goes down some ways, freeze and let sigils kick in, continue... The thing is, mage armour is terrible so even a 2* 180 hits around 350 ish on me. Sigils is basically why the mage class is considered the most expensive.
You can forgo the sigils for restos but you would use so many and sometimes they can't even keep up. Sigils aren't completely necessary, as evidence by me, but then for energy you would need to max energy boost (40 points at 180) and soloing is out of the question. One little bonus is that mages are great with groups and duos but you may not always get a group.
If you do or already have made a mage and intend on pushing through, I wish you luck. Basic tips would be stick with firemage, don't auto, don't add points in str, and generally keep energy equal to or above the amount of health you have.