share 3G connection on iMac via Linksys router

hello there

after reading many tutorials on the subject and not getting it to work on my system, I wanted to ask you guys if you could help me setup the following thing:
sharing an internet connexion from an huawei 3G stick plugged into my iMac via a Linksys router connected via ethernet to the same iMac.

I have tried like this:

• I connect the 3G stick into the mac and use the builtin software from my ISP to connect to internet (I basically enter a PIN and then click connect and I am online)

• then I go in "system > preferences > sharing" and then "internet connection"

• I select the connection from "Orange bla bla bla" (with is my ISP) and to "ethernet"

• then I go into "network" and I see the "Orange connection" from the 3G stick (with an IP like this one: 31.60.xxx.xxx)

• I go in "ethernet" and I try to configure it how I was adviced to (which seemed to work for others but not for me):

• I configure the ethernet to "manual", put an "IP" like this one 192.168.0.50, the "subnet mask" to 255.255.255.0, the "router" IP to 31.60.231.148 and the "DNS" servers to those that I found in the Orange connection under "advanced" (194.204.yyy.yyy and 194.9.yyy.yyy), then I hit save and go on with my Linksys router

• I first connect to it via its IP 192.168.1.1 and disable DHCP

• Then I connect it to the ethernet cable coming from my mac and here is my problem: it doesn't work

after trying various configurations (enabling DCHP on the router, adding the above DNS in the router configuration, etc), I cannot figure out what I doing wrong

Do you guys have a clue?

Thank you in advance for any help