I'd not even bother with frosties or necros, id make your bro go spiders fast and you go ghouls fast and just keep upgrading and hhing and get maxed ghouls and spiders you should own pretty nicely..
not necisarily, mass spiders have not proven effetive to me, ur strat would work nicely if the oppenents go air, and the web let the ghouls rape them, but if one of them mass human casters, u r dead, or if they both go ground ur dead