Nice summary. That's what makes enterprise sales challenging and time consuming and why Steve Blank spends a lot of time in his book explaining how to navigate it. What are some other common objections/challenges you've run into and how have you overcome them?
I'll keep the response specific to sales objections that a growth stage startups face
Scalability objections: can you scale to our volumes?
Respond with suggestions for a phased roll out. Take your backend expert in to the meeting and present credibility on why you can scale.
Company objections: will you be around for long? What if you get aquihired?
Reiterate vision behind why are doing your startup (hopefully the right reasons). Talk about your investors and the expectations/commitments made.
Control objections: "We are uncomfortable giving up control over this part of our tech stack"
Try to create analogies. Understand other parts of the stack that they have given up control over and why they feel comfortable with those. Feed those expectations back as contractual commitments that you are comfortable making.
Yes, I was wondering about sales objections, thanks. Those are good ones. What about resource constraints to integrate? This is one of the most common I've run into. Even if integration is as simple as a copy/paste of some code, it still requires moving ahead of their pipeline. To help here, focus on making it as easy as possible to integrate and also help the customer see why it helps them to make it a priority by showing the benefit of adding now vs. later (ROI data). Have you heard similar objections or are you only pursuing customers that have already reached out to you and have thus, presumably, already determined file upload is highest priority?