Dynamics D365 Finance Integration

I am in need of some integration work between D365 Finance and a local SQL application. I am proficient in .net, javascript but not in D365. I have a local legacy sql / asp / .net system that used to integrate into in-house AX 2012 R2 which has been migrated to D365. Initially I need to achieve some basic D365 integration to retrieve customer/supplier data and post journal entries. The development is in 3 areas as follows: 1. Customer/Supplier updates. I want to receive updates to customer/supplier account details/addresses ideally "pushed" from D365 when they are made , eg if an email address is updated or customer goes "on hold" etc. the customer data is sent over. I could possibly make do with a "pull" query on demand instead if necessary - unless I can just "pull" updated records since the last "pull" if this is simpler than a "push" (eg first ever query gets me everything; any query afterwards only gets me updated data). The format of the received data needs to be something I can use to parse and update the local sql database, so JSON, XML etc but not via CSV files. Ideally this would be a stand-alone app that I can leave running and it just polls for / receives updates. I would enhance it to insert the received data into my local database. 2. Customer Summary: Query all customer records to receive, for each customer: credit limit; YTD totals; outstanding balance; overdue amount; on-hold. I would run this query on demand and expect a simple data set with, for example, "customer ref", "credit limit", "ytd", "balance", "overdue", "on-hold". Data set to be JSON, XML etc. for me to parse. Ideally this will be a separate app that i can schedule to run as required. I would enhance it to submit the received data into my local database. 3. Insert journal entries. I need to submit journal entries on demand into the general ledger. So I would want to simply send (for example): "user", "customer/supplier ref", "transaction date", "nominal code", "amount", "description", "vat code" (and anything else that is required). I am not planning to use the invoicing / purchasing parts of D365 so don't need to be concerned with that. I just want to split my invoices by Nominal code directly into the GL. I already have a separate invoice / purchase system the output of which will be sent to D365 and remain as "draft" entries for approval. I would enhance it to retrieve the relevant data from my local database for submission to D365. I do not (ideally) want to have to create local csv files to then import into D365 but could consider this if absolutely necessary (as this may be quite frequent). I would also like to receive a "success/fail" response for each GL submission (or record ID etc) so I can record this against my local data (this could not be done if I have to use CSV files). This would be a separate app that ideally stays running and has an interface I can call to "start processing" Hopefully that is a sufficient overview with enough initial detail. Tim