I am looking for a possibility to add a number of conditions to an offer that must be met before the offer can actually be converted into an order.

In my case it is a quote for building garden sheds. Drawing up the quotation is not a problem and is neatly sent to the customer.
Converting the quotation to an order (to actually plan to build the garden shed) must meet the following conditions:

1. Quotation has been approved by the customer (signature)

2. A down payment by the customer  

3. An approved building plan (via another internal department)

4. In some cases: a building permit (based on the approved building plan)

NB: It could take up to 10 weeks in durations before all these conditions will  be met.

The intention is that on the relevant quotation page a few buttons are added with which the status of these conditions can be indicated. Only when all these conditions are  satisfied, it becomes possible to place an order for it.

How can I realize this in Odoo (v12)?