It all depends on your actual build and what you are hitting. If you replace another building by a tower, be prepared to get a noticeable plunder drop. Basically it will amount to 1/buildings times your plunder. At least 500k plunder loss on haunting (ally bonus plunder loss). If you build a tower onto a new, free land, you'll observe a small drop in plunder.
I will either be replacing level 4 guilds or putting on new lands.Havent decided if I should put towers first or last
It depends when you need them Place your towers as late as possible as you will want to delay your loss in plunder as long as possible.
How do osw's normally get started? Is it just something mutually agreed upon or does it begin with an argument or is it just my clans better than yours?
Most of them start with someone mouthing off about another clan, ally hires, excessive hits, etc. When somebody says it was for no reason, they are full of it. There's always a reason.