now i have a XGS-PON connection with a 5X router i can answer my own questions.
1. I’ve tried the modem mode link with an ASUS router and it does not work. Assume we have to wait for a firmware upgrade.
2. The cable is single mode.
3. In my installation the fibre lead come from the external brown box direct into the router. Some installs show an internal white box. The Virgin engineer did give me an adapter allowing me to extend the fibre lead. You can buy fibre leads cheaply from Amazon and female to female adapters.\
4. My ping is 12ms. Higher than i’d hoped but lower than DOCIS connections locally. I live in North England so this maybe why my ping is not low single digits.
5. The 5X has not crashed and speed has been reliable. 1.1GBs down and 110MBs upload. The only issue i have noticed is the UPNP getting confused with my PS5. Sometimes it does not release the ports when the PS5 is provided a different IP address. I’ve reserved an IP for the PS5 now to avoid this.
6. I am using the 10GBS port connected to a D-LINK switch with a 10gbs uplink. The D-Link has 4x2.5GBS ports allowing my to connect my laptops with a Belkin USB-C 2.5GBS adapter providing my laptop full speed access at 1.1Gbs.
7. I now also have a Virgin Stream box for TV which works very well. Channel flicking is fast without any buffering. Box has frozen once and required a power reset.