What units to use as games goes on

[rollems]

1) Is Royal Snake ok to use as Damage Dealers. Fairies and Dyrads as you said are only Lvl 1/2.
if you see in the screen shot i provided above. what unit shall i replace. i can get 1 green dragon right now.

2) Is there a place where i can add more archmages. i got only 3 from scarlet lost 1. so where do i get more.

3) Is it ok if i stick with this for a while. or shall i change my army. i just got Rusty and Verons opened but all the enemy there says lethal/invincible/very stong.
2 Archmage
1 Green dragon
40 royal snakes (guess i can get more)
25 repair Doids
25 Gaurd Droids

4) when i visit equipments most of them say Race: Human shall i buy them ? my army is mentioned above. will the equipment saying Human help Nuetral ones too ???