Customer webportal options?

Navitrans_fvet

The current situation for one of our customers is as follows:

- Heavily customized NAV 5.0 database
- Database is constantly evolving (new objects, extra users, ...)
- Possible NAV 2017 upgrade is only planned to start end of next year
- Extranet page with SSRS report accessible by their customers

The requirement - by end of this year - is to provide a future-proof 'tool' (customer portal) for their customers to share / access information.
Their customers need to be able to:

- register - limited - data into the database (provide a number of data entry forms)
- search for information (provide a number of data overview forms)
- get a quick data overview using charts (in replacement for the SSRS report)
- access this customer portal from anywhere and any device (having an 'app' / responsive website is mandatory)
- (Nice to Have) Upload / download documents

Knowing the conditions that customer is still on NAV 5.0, what are the options to meet the above requirements in the limited timeframe available?

- Perform technical upgrade to NAV 2009 R2, allowing use of webservices.
- Create a custom responsive website (from scratch) using webservice communication. Full customizable. Timeframe / budget would be a killer in here.
- Build a solution in NAV 2017 (gives faster result as far as web / app access). Very customizable. Adds an extra complexity to communicate / replicate with the current NAV 5 database. Requires a NAV license update, which is not really an option (due to possible license updates on current NAV 5 version). Might be costly based on the number of external (limited) users required. (https://dynamicsuser.net/nav/b/peik/posts/turn-the-dynamics-nav-web-client-into-a-customer-portal-in-two-hours)
- Sharepoint integration (with NAV 5)
- Look for a NAV add-on (Anveo? Armour?) - Is it really extensible to integrate charts / Power BI / ... Would this be a future-proof option?

PS: What would be the answer in case the customer was already running NAV 2017?