300k Warriors? No.

Send one wave of 100k Warriors, will get 35-60k losses. You can use any hero that has at least 100 attack+. Send spamming waves of 10k Warriors. At the beginning of your spam wave, respear it with a 50k warrior attack. If you have Feasting hall lv 9, thats 180k Warriors. If lv 10, thats 190k.

Capturing a lv 8 is important IN AGE II, because 1. Sometimes Historical Heroes are there, and 2. If you want the Queen/King, you need to capture a lv 8 NPC as that is part of the quests.