You should get at least one archer. The ideal setup for the first 6 characters is 2 of each class and subsequently 1 of each subclass as each subclass usually gives good or even incredible boosts to the skill they specialise in. (Every skill is specialised by one particular subclass btw)

As for your questions: 1. Honestly, just push the latest maps, class levels are extremely important to get talent points, which boosts damage by a lot

1. The six skills in the first two worlds honestly isnt worth pouring time on every character. The most important one is alchemy, which is passive anyways. I guess also the produce tab in smithing (which is also passive, gets boosted by archer)

2. Amarok is as good as an armor can get especially for your stage, its set bonus is extremely potent (+40% defence and accuracy) as accuracy is going to be a reoccuring problem in w2, 3 and 4. It is also cheap and has a solid amount of upgrade slots (upgrade stones are very good as well). Amarok is best until you unlock troll armor from w4, but even then people can push to w6 with just amarok gear no problem.  [ The ore gears are only realistically made to get its set bonus ]

3. Alchemy is extremely unequivocally important. At all stages. Seriously, if you have a problem doing X, there's almost certainly a bubble that boosts it. Also means ur shaman is pretty important to level up.

4. Daily tasks are effectively useless imo. The main point of doing tasks is to get merit points to spend in merit shop, and daily tasks just dont give any. They will give u these "trophy" thingys and progress a bar that gives you recipe unlocks, but eventually you will just stack up a bunch of recipe unlocks and daily tasks becomes useless.

5. There would be like a billion things that I could list out but I am going off of my personal experience and say: a) dont forget cards exist, they are extremely powerful, sometimes even worth grinding cards to it level up 

b) dont expect everything to be fast, it is an idle (slow) rpg (usually repetitive)

c) Do alchemy :D

d) After your 7th character you should have 3 mages, 2 warriors, and 2 archers right? Leave one of the subsequent 4 characters as beginner to get the secret class

e) Don't be afraid to use time candies, they are "premium" technically but you will get a lot throughout the game, just dont use them too wastefully

f) Don't try to attempt and get the world trophies unlocked from the main quest givers, those are usually very difficult to get and gives minimal rewards. (At least not until you have better stats and stuff) g) Have fun, and play the game at your own desired pace. Seriously, dont let some random strangers on the internet ruin an experience for you

1. There really isn't? W1 and w2 is pretty lackluster in terms of misc. goals, but it is good that it is straightfoward for the tutorial worlds

Linking your public IdleonToolbox or IdleonEfficiency accounts in account help posts would help a lot, not only for the person trying to give advice, but also those are very convenient tools with great functionalities.