Smoking meat or fish was originally done as a way to preserve it in times of plenty for use later when fresh food was scarce. The preservation was achieved by removing water from the food that the bacteria need to grow (by the addition of salt and air drying) and through the antiseptic properties of the smoke itself. At some point it was discovered that certain salts (that contained nitrates/nitrites) made the food even safer although it was probably not understood why at the time. Over time many different styles of smoking were developed leaving us with the variety of regional foods that we have today.
As you say, cold smoking food is not rocket science once you understand what is actually happening. The primary purpose is to prevent the growth of harmful bacteria and spores whilst the food is stored. These days this is usually achieved using a combination of the following methods
The reduction in available free water. This is initially achieved through the initial curing process by the added salt and sugars in the cure drawing water out from the meat/fish. Later in the process this is further reduced through the smoking process or by air drying.
Increasing salinity within the food. In order for bacteria to live/grow it needs to be within fairly narrow salinity range to maintain its metabolic functions. By increasing the salinity within the food the bacteria will either be killed or their growth will be inhibited.
Increasing the acidity. Many of the harmful bacteria cannot grow in acidic conditions and so by reducing the pH (increasing the acidity) through the addition of acidic ingredients (e.g. citric acid) or through the introduction of harmless acid-producing lactobacillus cultures. This is predominantly used in the production of salamis/chorizos etc.
The addition of Nitrites. Nitrite is used to control bacterial spore germination that are not managed through the other methods - primarily Clostridium botulinum. Nitrites also help give the food that characteristic pink/red colour. Over time the NItrite will break down and become less effective and so in foods that be stored for long periods of time Nitrate is also added. This is slowly converted to Nitrite and so maintaining the levels. As Nitrites are toxic to humans in fairly small amounts it is therefore essential that they be used carefully and that you know the amount that will remain in your end product. We should not get paranoid about this though as over 80% of the Nitite in the average western diet actually comes from eating vegetables.
The use of smoke. Although smoke is a mild antiseptic its primary purpose today is as a flavouring. In sufficient quantity the smoke will help inhibit bacterial growth on the surface however for foods such as fish the greater effect is by the air flow over it during the smoking process leading to further water reduction.
Some general pointers to help you get started and also some links. You will find a lot of very helpful advice on each of these by searching through the forum.
It is always important to ensure you practice good food hygene - however it is especially so when preparing food that is going to be cold smoked and subsequently eaten uncooked
Cheese - Most hard cheeses do not provide suitable environments for the harmful bacteria to grow easily. As has been said above you do not cure cheese before it is smoked. Cheese is best smoked at about 50 - 60 F and usually 2-3 hours in the smoke is sufficient. Once out of the smoker leave the cheese in the fridge overnight to allow the surfaces to dry before packaging. Once smoked the cheese will take 2-3 weeks for the flavours to mellow and for the rounded smoked cheese flavours to develop.
Fish - Most fish will need to be cured before smoking to reduce the moisture content however this does not usually require the addition of any Nitrite. Salmon is one of the most popular fish to cold smoked and it provides quick reliable results. The salmon can be lightly smoked which will need it to be subsequently cooked or it can be traditionally smoked after which it can be eaten uncooked. Both methods are essentially the same however the result will depend on how much water you remove from the fish during the process. Be sure to weigh the fish before you start the cure so that you know how much water has been removed. In order to produce the traditional smoked salmon you need to reduce the weight of the fish by between 15-18%
Bacon. This can either be wet brined or dry cured before smoking and this will usually involve the addition of Nitrite. I prefer to dry cure my bacon however you will find a lot of good methods for both on here. When using Nitrite just be certain of the amounts that you are adding and weigh it out on accurate scales rather than use spoon measures. Until you become really comfortable with using Nitrite it is best to buy a ready prepared cure salt (like Cure #1) that can be more easily weighed out and added to your main salt and sugar. You are looking to end up with a maximum residual Nitrite concentration of 175-200 Ppm in your end bacon (usually less) and please don't be shy to post up your proposed cure mixture here for checking before you use it. There are several of us who can double check your calculations and Dave Omak is the king of cure calculations on here. Do not add cure that also contains Nitrate when making bacon as Nitrate will potentially form nitrosamines at the high temperatures in the frying pan, which has been linked to cancer.
The levels of Nitrite are important but so is the overall balance of salt and sugar. You need to be aiming for about 2-2.5% salt. The sugar content will depend on your own tastes. If you add too much sugar though you can end up with burned caramel flavours in the pan when the bacon is cooked.
If dry curing, rub the cure into the surface of the pork before putting in the zip lock bag or vac pack and be sure to add all of the remaining cure before sealing.
Sausage/salami. There are so many varieties of these and it is best to search for any that you want to make on here or in reputable curing books. These usually employ all of the above curing techniques. Important things to remember are, as you are dealing with ground meat you must keep all of the ingredients chilled throughout the preparation process, until the point where you add any lactobacillus cultures (when creating a fermented sausage). The drying process for these are very important as drying too rapidly will result in the outer surfaces of the sausage becoming hard. You really need a humidity controlled drying environment to produce these effectively.
Generally when smoking any food it is important to manage the temperature within your smoker as it is very easy to let it get too warm. In the winter it may actually need warming though as it can get too cold. It is also very important to keep a good air flow through the smoker at all times. This helps to remove moisture and also stops the build up of stale creosote flavours on the food.
This was not meant to be a detailed guide on cold smoking techniques but just a bit of additional background and some general hints to get you started.