"which do you consider the best faction traits?"
Enchanters, possibly Decalon if I'm playing a faction with Creatamages (Henchmen or Sions), Master Archers if you want to play with Archers, Masterwork Chainmail because I value 4 initiative more than ~5 defense. Really depends on what you want to play your faction as, though - there are all kinds of very strong combinations you can come up with.
"Is wanderlust (quest maps) worth it"
If you want a decent way to level champions up later in the game, then yes. If you don't really value champions beyond the second guy you give an army to and don't really care if they don't get much beyond the mid-teens for their levels, then it isn't really valuable.
"Is having the rebel trait very bad?"
Not really. Unrest is easily managed, especially once you have a few high-level fortresses other than your troop recruiter, and you should have enough unrest reduction with Bell Towers/Clerics/etc, as well as unnecessary champions, to keep unrest at manageable levels even without the high-level fortresses, unless you like to keep taxes high.
"Which are the best professions for a character"
See here for my opinions on the matter: https://forums.elementalgame.com/444783/page/1/
I did neglect to mention Scholar, which is more of a mid-to-late game profession which I don't think is terribly useful; on the other hand, it's not almost useless like Bandit Lord and Hunter are.
Beastlord is a very strong profession, if you build your character as a curse spellcaster, and might be the strongest profession in the game, depending on how you play it. On the other hand, if it fails you against a creature which is strong relative to your army, you might be in a fair bit of trouble, especially early in the game. Warlock is a decent profession for a damage mage in the mid-to-late game, while Armorers make great army leaders, especially if your units have high defense. Most of the others are more or less middle of the road, in my opinion.
"Can the items that lets you get rid of enchantment upkeep be aquired in another way later on in the game?"
Yes, but only by forcing a sovereign bearing the item to surrender to you.
"Is there a maximum level for a hero?"
Sort of. As phazonfreak said, heroes continue to gain levels until they run out of traits, and possibly beyond (some people in the past have said that they were able to raise their champions to levels where they no longer had any traits available to take, and keep going, though this may have changed in a patch and I've never leveled a champion that far myself). However, as you may have noticed, each successive level requires more and more experience to attain, which tends to result in champion levels more or less stalling in the mid-teens in my games. You can continue to increase the champion's level, but it continually becomes more difficult to do so, and the experience required appears to increase with the square of the champion's level. Besides that, experience earned from fights is inversely dependent on the strength of your army, which is in part dependent on the level of the units in the army, and champion levels count a lot towards army strength (more, at any rate, than unit levels do, though how exactly the battle experience value is calculated is unclear, so don't ask for specifics from me).
Which blood do you like most?
Amarian, Mancer, or Altarian. Amarian for the bonuses it gets from shards and for the spell ability it grants to all units of that race, Mancer for the movement bonus and the road building trait, Altarian for the Henchmen and the Rush ability.
Amarian Blood - +1 dodge per air shard, +1 initiative per fire shard, +1 spell mastery per water shard, +1 spell resistance per earth shard. Grants the Soul Spark spell, which deals 2 (+1 per level) lightning damage per figure in the casting unit to an enemy target; spell is ranged but costs mana (which I think is also multiplied by the unit size). No extra unit design traits.
Altarian Blood - +10% to experience gain. Rush - unit gets to take an additional action. Unlocks Henchmen with Henchmen technology. Unlocks the 'Potential' unit design trait, which grants +25% experience gain for +8 production cost.
Ironeer Blood - +50% mana cost for tactical spells. +30 spell resistance and +1 HP per level. Unlocks Iron Golems with Blacksmithing technology. Grants the Guarded Strike unit ability, which makes a half-damage attack that leaves the attacker in defensive stance. No extra unit design traits.
Mancer Blood - +1 accuracy per level, +1 movement (both tactical and strategic). Grants the Road Building unit design trait which allows trained units to build roads for +0 production cost. Grants the Experienced unit design trait which grants the unit +1 level, but increases the upkeep by +1 gildar per turn and costs an additional 25 production.
Tarth Blood - +3 attack and initiative in armies of three or fewer units. Grants the Double Strike unit ability, executing two attacks at 20 less than the normal accuracy. No extra unit design traits.
Krax Blood - +8 defense when at less than half health. Grants the Fortify ability, which creates a Fortified tile on the tactical battle map that grants +10 accuracy and +20 dodge to any unit in that tile. Doesn't grant any extra unit design traits.
Wraith Blood - +20 dodge per level, - 1 HP per level. Grants the Wraith Touch ability, which transfers 1 HP per level from the target to the caster; damage is multiplied by the number of figures in the casting unit but can be entirely resisted; target must be in melee range. Grants the Hallowed Rites unit trait, which grants +3 mana per unit killed by the unit with this trait for an additional 8 production cost. Grants the Zealotry unit trait, which grants +3 initiative and -1 HP per level, costs 8 production (really bad trait - your units won't gain any health from levels if you put this on them).
Trog Blood - +2 Attack if at under 50% health. Grants the Berserk ability, which increases the unit's attack and initiative by 2 but places it under AI control; spellcaster units which are Berserk will not use spells. Unlocks the Juggernaut special units. Does not grant any extra unit design traits.
Urxen Blood - +2 Attack if in an army of five or more units; units receive double the usual swarm bonus. Grants no extra traits or special units.
Quendar Blood - +50% Fire Resistance, -50% Cold Resistance. Grants the Dragon Tongue Flame ability, which deals 2 fire damage per caster level to targets in melee range; damage is multiplied by number of figures in casting unit. Grants access to Slave units. Does not grant any special unit design traits.
Also note that all Empire factions can produce Sions, which are essentially lesser versions of Henchmen. An Altar-blood Empire can have limited access to Life Magic through the Life Adept line of Henchman traits. Empires can be of any race, but Kingdoms are restricted to Altarian, Amarian, Ironeer, Mancer, Tarth, Krax, and Wraith blood.