First Time Building

Hello, I have some questions regarding building. My wife and I will be acquiring 5 acres in the southern portion of thurston county in Washington state. It is raw land with a transformer close enough to the proposed build site to be able to negate costs along with the ability to install both the water pipe from the well we would have to have someone dig, and also conduit from the transformer to the proposed house site. We’re seriously considering hiline homes, not so much for the build quality, but for just getting the house to where we want it for the price. My big question is that, we have approximately 80k cash that we have to work with and our lender says we need to come up with 10% down in either improvements to the land with receipts, or liquid cash, is there any other pieces of information that I’m missing. We’re wanting to keep the house under 470k in total, but we’re concerned with the price of permits being unknown, along with having to do the improvements and pay someone to log the land, that we will go over budget. I apologize if this is a dumb post but this is the first time we’ve ever dabbled in this. Thank you