@Miles80 

When you run Deco mesh in Access Point mode, these options (LAN IP, DHCP Server, Address Reservation) are on ISP router, not in Deco app. You should have access to configuration Web pages of your ISP router, and this is where you need to configure these settings.

>What is the solution to support 100+ devices in the whole motel?

I can give you basic recommendations, but if these will not be enough you may wish to find IT knowledgeable person nearby and let them tune your ISP Router/Deco mesh. 100+ devices is above regular household solutions, may need professional approach.

Nevertheless, here are my recommendations. I assume most of these 100+ devices you mentioned belong to guests.

1. Configure short DHCP Lease Time, start with 30 minutes and drop to 15 minutes if not enough. (ISP Router)

2. Set IP range to multiples of number of active devices. Start with at least 200, but if router can handle more you may wish to go up to 400-500. (ISP Router)

3. Enable Guest Network in Deco app and provide guests and visitors with Guest Network SSID/password only (Deco app)

4. Connect your smartphone and other trusted devices/phones to Main Network. Don't share Main Network SSID/password with guests and people you can't trust. (Deco app).

5. Make sure Main and Guest Networks are separated from each other (Deco app, More/Guest Network/Advanced, make sure Allow Local Access set to disabled)

6. Disable "MAC address randomization" on your smartphone and configure IP address reservation on it. Even if ISP router runs out of IP addresses, your smartphone will stay connected. Do that for all other trusted devices. Devices such as SmartTV may not have MAC address randomization and can just be configured with IP address reservation (ISP Router)

7. For better Deco mesh performance, DO NOT pass all traffic through Main Deco, instead, this type of network layout is recommended:

If you need clarifications on my recommendations or have follow up question, feel free to ask.