Part of the reason I started working at Stripe is that I remember going through exactly this and it freaking sucked. Building a product and finding customers for it is hard enough without also having to cross-class as an expert in international taxes of software sales.
(Drop us a line if you need a referral to an accountant; we can introduce you to an accountancy that works with a lot of Internet businesses. We also have some guides about it at https://stripe.com/atlas/guides to demystify it a bit.)
We have a number of accounting firms which we work with that we refer Atlas customers to. This lets us explain the Atlas concept once, prepare the firms for "You're going to have a high volume of companies who will often have the same set of issues so let's research and brief those in advance", build out tools to assist with information gathering, etc.
It also lets us help refer companies to accountancies whose sweet spot most closely corresponds to the facts of the company.
(Drop us a line if you need a referral to an accountant; we can introduce you to an accountancy that works with a lot of Internet businesses. We also have some guides about it at https://stripe.com/atlas/guides to demystify it a bit.)