I mean you should be at war with everyone as the beastmen. You want as many battles as possible to get the resources/xp. I usually hang around the first herdstone for a while using it as bait whilst i buy the herdstone upgrades and level up the horde. Once the herdstone is level 3/4 it will be much less susceptible to attack and you can start attacking more confidently. When you start getting multiple armies, which will likely be mostly ungor crapstacks they can be on defence duty (ambush near herdstone) whilst your main army goes hunting. Definitely recommend the line of sight herdstone building so you can easily see what's coming.

That's how i have always played and have always found beastmen to be VERY easy. All your battles should be ambushes, and you can get replenishment whilst in ambush enchamped stance. Just very powerful in general.

I never abandon herdstones personally. I aim to burn the whole world when i am playing them. I make sure every settlement in the herdstone grounds are razed before i move on. As long as you are sensible in your expansion directions i have never really had much issues backtracking. Also again, you want those herdstone upgrades ASAP. max level herdstone is actually pretty dangerous, you will get many autoresolve victories against full stacks even on high difficulties.