What you need is a dual probe electronic digital thermometer. One probe watches the smoker temp the other the meat temp. Sausage smoking requires very close control on your smoker temp. and slow increase in the temp as you smoke. Most sausage are cooked when the internal temp hits 150 F some go to 160F the smoker temp should not be over 175 F or the fat will render out of your sausage and it will be grainy dry like sawdust.
Normally start at 120-130 F with no smoke for about 2-3 hrs, this will dry the casing and allow smoke penetration. Smoke won;t penetrate a wet casing. Increase the smoker temp to 150 F and start smoking, when your sausage gets to say 140F internal increase the smoker to 175F and continue to smoke to an internal of 155F. How long this will take depends on how big your sausages are, but count on 8-12 hrs to get the job done.

As far as a smoker I prefer a propane powered smoker as they have the oomph to smoke during the cold weather, electrics just aren't powerfull enough.
Get a large smoker some of the small models can't get below 250 F which is useless for smoking sausage. They need to be altered with a needle valve between the propane cyl. and the burner.

You already heve your venison and pork mixed. For a good sausage you need 20-30% fat content. Pork shoulder is about 25% fat so if you mixed it 50/50 with venison you will have 12.5 % fat thats way too lean for sausage and it will be very dry. You need to add the proper amount of pork FAT to bring your mixture up to 25%