Reverse proxies can have a negative impact on page speed. It is difficult to completely answer your question without additional information such as:

Why is there a reverse proxy at all?
How significant is the performance degradation?

If you are interested, I can get on a call with you.

Yes, this is possible. I am an active stakeholder in an organisation that has developed high performing voice apps and is currently building fitness apps (skills) for Google Home and Amazon Alexa.

One of the easiest ways to start is from the following link:

https://developers.google.com/actions/dialogflow/first-app

There is a lot of nuance in this upcoming field of Voice Development. If you need further answers or would like a call then please connect with me.

To a large extent, the skills required to develop an app have become commoditized over the past few years. Also available, are a large number of templates to kickstart app development (specially games). That being said there are some key issues which differentiate successful apps:

User Acquisition:
- Organic
- Paid (at a price that gives best ROI).

Sustained Development:
- Ability of the developer to consistently make changes based on user feedback. I think that app development really starts after the first version is released to the market.

Customer Support:
- How well can the developer interact with customer and build a community.

These are my immediate thoughts.