when do i know that im ready for first boss?

[alpinar]

i have discovered moste of the islands and i really want to kill the spiderboss wich i supose is the first 1(on devir island it is i think)...i tryed at lvl 21 but failed epic..the spiders were overswarming me not to metion that he hited me like a truck(im a mage on normal mode btw)..now im lvl24 with

about 7k -leadership
3 blackdragons
3greendragons
7 orcs
34paladins
37 shamans
my question is if i have any change or should i keep lvl upp and improve my spells and get bigger units.will be thankfull for any tip