I can see the upside for many things, but you can do that efficiently, not costing 5 figures.
The only risk I can see is the lack of managed services, but Postgres isn't that hard to manage yourself, and other value-add AWS services can still be used (the cost savings of your baseline load being on bare-metal would most likely still offset the bandwidth costs of moving data between AWS managed services and your bare-metal host).
For SNS, what does it offer that RabbitMQ doesn't? I've always found RMQ to be rock-solid and wouldn't use SNS anyway.
We had migrate our servers 4 times as hosting company kept changing things, then getting purchased by IBM, then IBM was trying to figure itself out.
I didn’t kill the company, mostly due to a lot of really hard work. But it came close.
If you instead use cheaper 3rd party hosting companies, you may have hurdles to growth and future migration cost since those companies do not have many of the certifications required.
From an investor POV, paying a little extra now is often worth it to reduce risk and remove barriers to explosive growth.