On A: Using a p3.2xl for that task leaves you with a minimum ec2 cost of goods sold of 50 cents per user per month for the target task. To make a reasonable SaaS business out of this you would need to be charging a minimum of $5.00 per user month for the service that this GPU is providing, assuming all other tasks have a negligible impact on Cost of Goods Sold, and that you are able to spread the load optimally throughout the day - and thus don't have to purchase higher capacity during peak.

This isn't too bad of a situation if this GPU provides 100% of your value proposition. but, if you needed your product to perform 5 such tasks - or competition/customer demand forces you to move to a bigger model with a 10 words per second inference rate then you may find it hard to balance customer value vs. price vs. margin.