I am projecting here, perhaps, but I think the question you're asking is "why doesn't my salmon come out moist and succulent like what I get at the store?"
A couple reasons.
First: you want to properly cure the salmon for at least 24 hours beforehand. 36 is better. To cure, you will need two whole sides of salmon (or one cut in half), with the skin on. Rub your cure into the flesh--so 2:1 salt:sugar, plus whatever other spices you care to use. The addition of brandy sounds lovely; I like tequila or a nice peaty/smoky Scotch myself, or maple syrup (but obviously nix the sugar if you're doing that). Place the two pieces together, flesh to flesh, optionally including herbs between. Wrap very tightly in plastic, completely sealed, bung into your fridge to let it cure.
Second: when the fish is cured, remove from the wrap, rinse off the cure.
Third: time to smoke. If you want dry and flaky, hot smoke--this seems to be what you're doing and what you don't like. Therefore, it's cold smoke time. The two basic ways to do this are either to add LOTS of trays of ice to the smoker itself, or to route the smoke through a cooler filled with ice and then back into your smoking chamber. A quick Google should provide you with diagrams for doing so.
Do not over-smoke. Fish picks up flavours quite readily, and will dry out if oversmoked, even if cold. Really for salmon I don't think you need much more than 20 minutes of cold smoke.
1- The meat drying out is a very real problem when cooking for so long. When I have smoked with water it has seemed to be less of a problem. I'm sure it also gives a nice thermal buffer but I haven't conducted experiments on this.
2 and 3-
When I built the AB style smoker mine was smaller and earthenware so it would retain heat better. My cheap little hot plate was not able to get the temperature up to even 200F.
With a bigger smoker and one made out of metal I don't think a normal little hot plate will be able to get hot enough. You can experiment of course. It may be that my cheap hot plate was just under powered.
In my smoker I adjusted the hot plate temp knob as necessary. Eventually of course it stayed at full on.
If you are interested in more of a project- there are many hobbyist projects for making temperature controlled smokers. They would be more work but for an excellent reward. I was just looking at this one today that uses a wireless router for a web interface and an Arduino for control. Kind of like a homemade sous vide setup but for a smoker:
http://tvwbb.com/eve/forums/a/tpc/f/9270072103/m/5721075126
Best Answer
I have successfully smoked with apple wood chunks wrapped in foil in my outdoor grill. The trick is to find a setting that will maintain ~300 F using 1/2 of the burners. Then place the foil-wrapped chunks on the hot side and the meat on the cool side. The wood will begin to smoke after 10 minutes or so.
Keep checking periodically to maintain 300 F.
I do this with already cooked sous-vide pork. It may need adjustment to cook raw meat while smoking - maybe up the temp to 350 F or so.
I adapted this technique from Kenji: http://www.seriouseats.com/2016/08/food-lab-complete-guide-sous-vide-barbecue-smoked-bbq-brisket.html: