I’ve had some time to devote to this, so insights for those who would also like to start the service.
For synthing I followed the procedure for openwrt:
I didn’t address WAN access, I don’t need it. initd can be run via luci. I ran the command in ssh and the service is running:
[TT674] 10:25:24 INFO: Using the discovery mechanism: global discovery server https://discovery.syncthing.net/v2/?noannounce&id=LYXKCHX-VI3NYZR-ALCJBHF-WMZYSPK-QG6QJA3-MPFYMSO-U56GTUK-NA2MIAW
[TT674] 10:25:24 INFO: Using discovery mechanism: global discovery server https://discovery-v4.syncthing.net/v2/?nolookup&id=LYXKCHX-VI3NYZR-ALCJBHF-WMZYSPK-QG6QJA3-MPFYMSO-U56GTUK-NA2MIAW
[TT674] 10:25:24 INFO: Using the discovery mechanism: global discovery server https://discovery-v6.syncthing.net/v2/?nolookup&id=LYXKCHX-VI3NYZR-ALCJBHF-WMZYSPK-QG6QJA3-MPFYMSO-U56GTUK-NA2MIAW
[TT674] 10:25:24 INFO: Using discovery mechanism: IPv4 local broadcast discovery on port 21027
[TT674] 10:25:24 INFO: Discovery mechanism in use: IPv6 local multicast discovery on [ff12::8384]:21027
[TT674] 10:25:24 INFO: Ready to synchronize "Default Folder" (sendreceive)
[TT674] 10:25:24 INFO: TCP listener ([::]:22000) starting.
[TT674] 10:25:24 INFO: Relay listener starts (dynamic+https://relays.syncthing.net/endpoint)
[TT674] 10:25:24 INFO: QUIC listener ([::]:22000) started
[TT674] 10:25:24 INFO: Loading HTTPS certificate: open /root/.config/syncthing/https-cert.pem: no such file or directory.
[TT674] 10:25:24 INFO: Creating a new HTTPS certificate
[TT674] 10:25:24 INFO: Completed initial scan of sendreceive's "Default Folder".
[TT674] 10:25:24 INFO: GUI and API listening on 127.0.0.1:8384
[TT674] 10:25:24 INFO: Access the GUI via the following URL: http://127.0.0.1:8384/
[TT674] 10:25:24 INFO: My name is "turris".
[TT674] 10:25:24 AM WARNING: Syncthing should not be run as a privileged or system user. Please consider using a regular user account.
[TT674] 10:25:33 INFO: quic://0.0.0.0:22000 NAT type detected: symmetric UDP firewall.
[TT674] 10:25:33 INFO: quic://0.0.0.0:22000 resolved external address quic://78.80.47.85:22000 (via stun.syncthing.net:3478)
Accessing via localhost on the PC refers me to the service running on the PC > it´s ok.
Access to http://192.168.1.1:8384/ doesn´t work.
I had to change the address in init.d and the syncthing configuration file (and there change option enabled from ‘0’ to ‘1’. Stop/Start service and it already seems to be listening on the router address.

I’ve been unsuccessful with Radical so far. I have installed the packages for radicale2 via luci, including the luci interface and language pack. Following the instructions I have set up the basics via luci interface with output:
config section 'server'
option ssl '0'
list host '192.168.1.1:5232'
config section 'storage'
option filesystem_folder '/srv/radicale2/data'
config user
option name 'XXX'
option password 'XXX'
config section 'web'