DD - going to the trenches.
Well, you guys are not the ones that are responsible for doing the due diligence if you are getting bought out.
But, if you want to know some of details needed then I would have all of this information ready;
Financials - past, present, future projections
Detailed company information - revenue drivers, strategy, marketing strategy, how are you getting customers (paid / not paid ), how much revenue per customer, lifetime revenue, lifetime of a customer
Revenue driver margins, future revenue drivers?
Competitor analysis - what keeps you ahead/behind
Growth areas for your industry/business
All industry info - qualitative and quantitative
Porters 5 forces would help with getting to know a startup
Management team background
Advisor background
Current stock ownership, options, ect
Laws surrounding your product - what is the legal landscape, any pitfalls or shifts that will negatively/pos impact your biz?
Economics of the biz - costs, expenses, variable costs, ect
Operating plans
Critical risks
list of assumptions
Thats a bunch off of the top of my head - some of those categories hold a bunch of topics like 'fin statements' make sure you have balance sheet, cash flow, income statement, valuation model, ect.
Hope that helps, there is more..