You're going to have a tough time dealing with vehicles and mechanized armies with this list because you have no significant way to destroy vehicles at range and even in assault you've only got the one nob biker unit that can do it without disembarking. Adding in deffkoptas, warbuggies, or lootas can help with this, as could giving deff rollas and boarding planks to your battlewagons (though that leaves you in melta range which is not a good thing.)