NAV 2017/Dynamics 365 - data exchange with external web application. Web services?

Hi guys,

There is a SharePoint web-application which exchanges data with NAV using a 'buffer' SQL database (iDB).
NAV exports master data (vendors, gl accounts, dimensions, etc.) into iDB and imports processed accounting data (e.g. journal lines) from iDB.

In most cases NAV server & clients are located in a different network/domain than the 'buffer' database, in which case a VPN connection is established between the networks.

Data exchange is coded using ADO.NET in NAV.

We think about switching from ADO.NET to some other technology, which would not require a VPN connection between NAV server and 'buffer' database.
This is especially relevant for Dynamics 365 for Financials, since it would be an Azure virtual machine hosting the NAV and apparently it would not be possible to establish a VPN to it.

1. With this, please advise if it would be possible/good idea to allow web application to 'import' master data into 'buffer' db using exposed web-services in NAV?
2. Are there are any performace issues with using web-services for large amounts of data?
3. Will it be possible to allow the web-application to create journal lines in NAV using, e.g. exposed 'Purchase Journal' web-service?
4. What would be an alternative to using web-services in this scenario?

Thanks in advance and looking forward to hearing from you ;-)