After quite some hassle I now have a old hardware serving my internal network with DHCP and all clients can use my internet connection. The operator I use is Telia with a mobile broadband dongle.

1. Get the Internet broadband working with the Vodafone beta driver (Connect Card Driver Version 1.99.17 (Beta)). The only customization was the APN: online.telia.se

2.1 Create the internal wireless network. This includes the option to bridge a wireless and a wired interface on your internal network.

2.2 The above also includes connecting the Internet interface (ppp0 in my case) to the internal interfaces (wlan0 and eth0 in my case)

2.3 Set up a DHC server (DHCP Server 3) for creating the IP network internally.