I have fibre 100/100 Mbps WAN via my ISP, which has provided me a router of the brand "Technicolor". The router can create a Wi-Fi network, the 2GHz band uses 802.11/b/g/n and the 5GHz band uses 802.11a/n/ac.
I also have an older Apple TimeCapsule 2011 model with 802.11a/b/g/n on both bands.
I'm not proficient at networks, so I have for the past few years had the ISP router on the network at 192.168.1.1 where it does NAT and DHCP — and downstream I've had my TimeCapsule at 192.168.0.1 also performing NAT and DHCP to which I've had all my other network devices connected.
This configuration is Double NAT, which I have understood is bad or sub-optimal for P2P applications like BitTorrent, gaming, etc.
My reasoning has been that I don't trust the ISP/router manufacturer completely and that I would be safer with my devices behind the Apple router. But to be honest, this has been a loose assumption and I didn't have any facts to back up that a double NAT/DHCP configuration would be any safer than connecting all the devices to the first router.
Is there any benefit to having my devices connected to the second router; the Apple TimeCapsule? My primary concern would be security and any Apple "convenience" aspects such as Back to My Mac support, etc.
One disadvantage is of course that the TimeCapsule's Wi-Fi speeds are dated, and I have devices that can use ac speeds.
If there in fact are advantages to having an Apple router behind the ISP router, how should I configure the network to avoid Double NAT? It seems that the ISP router can't be set in Bridge mode, and I think the ISP wouldn't like it bridged as they sometimes access it for diagnostics and pushing firmware updates.