Hi,
We are a London based cloud hosting and development company. We specialise in hosting and scaling cloud based solutions.
For this project (ERPNext), we recommend Google Cloud (Compute Engine) as it allows you scale it at a much efficient way (especially in terms of pricing) than using App Engine. As you can see all our projects are hosted on Google Cloud and AmazonAWS (including our own website) and we are confident that we will be able to deliver the project within the time frame you have specified.