1. You must use a curing salt. Insta-Cure #1 or Prague Powder #1 is what you want. The proper ratio is 0.25% by weight of meat, or 4 ounces of cure for 100# of meat. You do not want cure #2, because it won't complete the nitrate curing cycle in the short period of time that it takes to make dried sausage.
2. Your total salt percentage should be no less than 2%. Ideally, it should be around 2.25%. This is to make sure the salt content is high enough for food safety purposes.
3. When you stuff the sausage it needs to be firm with minimal air pockets. Pop any air pockets with a pin.
4. A long stretch of dry days with low humidity is not ideal, but neither is a rainy stretch. Try to do this when the weather isn't one of those extremes.
5. You can hang the sausage just about anywhere. I've made dried sausage in everything from a dedicated smokehouse to a cattle trailer. Your garage will work as long as you can keep vermin and pets away from it, and you aren't storing your vehicle in the garage.
6. It's generally ready when the sausage loses 30% of its wet weight. Weigh a couple of the fresh sausages, tag them, and write down the starting weight and finishing weight. When they hit the finishing weight, they are done. This can take anywhere from 10-20 days.
7. If the sausage at its end weight feels hard on the outside, but looks raw in the middle, congratulations, you've got case hardening, and it happens to just about everyone that makes dried sausage at home. The fix is to vacuum seal it and leave it in the freezer for a month. It will even out over time.
ETA: if you want to smoke it, you only need to cold smoke it once for 3-4 hours. Once the casing starts to dry, it won't take anymore smoke. Also, a small fan will help with air circulation and promote even drying.
If you have any other questions, ask them.