I've been making differnt kinds of naturally fermented breads for probabl 25 years. I've also sold it for a living but it was tough. I still sell it in the winter
I never really had a problem maintaining cultures as long as I fed them every day or two, twice a week isn't enough really unless its pretty chilly. Some people claim you need to feed twice a day but I haven't found that necessary. The more often you feed it and the larger thouse feedings are percentage wise, the greater the ratio of yeast to bacteria which will aid in rising. Of course this also means its not going to be as sour. If you see liquid forming on the top you need to feed it. I keep some starters in the refrigerator but I've never like doing that if I want the bread to sour, well except for rye starters and thats mostly becasue they ferment so fast and the are easy to sour. If you have trouble getting the bread to sour you can also add some white rye in the early stages. Rye fements and sours vy well, much better than wheat
I've never had a problem with getting sourdough to rise, even with 100% rye doughs like Bavarian pumpernickel, though they are denser by nature. You don't want to ferment too long without building the dough. Its best to at least double your weight. Definatly autolyse the dough for at least a half hour before kneading. Personally I build bread over the period of a week but it doesn't take much work in the early stages. This builds flavor etc. Retardation, meaning refigerating the fermentiing dough, also builds flavor. You can manipulate the sourness, etc by temerature and by the consistancy of the starter. Generally solid dough starters are best (biga, patter fermente) but liquid ones like Poolish are more convienient and I do use them in some situations. When I use a more liquid starter I use just starter which takes a lot of starter. If you do it this way you have to know how much flour is inthe starter so you can get the proper hydration. Also I ALWAYS measure the major ingredients by weight. if its something small like some spices or sale I might go by volume but with flour it gets very deceptive to go by volume and also harder to step up.
There are many natural ferments which, although they could be called sourdough, aren't necessarily sour. I use a Desem starter for whole wheat which is a cold fermented starte of a dough consistensy, 100% whole wheat. Oddly enough, if you condidtion a starter to cold temps it will rise much better, though it won't sour much. This is becasue yeast grows much faster than bacteria and cold temperatures inhibit bacteria a lot more than yeasts. You can get bread to rise at 40 degress but it takes a while. If you decide to make a 100% whole grain bread using natural ferments it good to use techniques like soakers, which is kind of like making a dough without and ferment in it and letting it sit for at least 12 hour and up to 24 hours. You have to refrigerate it if you let it sit longer With this technique you make a dough starter, call it a biga and a soaker in place of the flour, water etc you would normally use. What this does is soften the bran which would cut the gluten and cause problems rising and als give the dough time to buildvery long gluten chains. I never use added gluten, you don't need it except in very rare cases like if you want a lighter 100% rye or something. I make a potatao onion dill rye which in which I sometimes use added gluten but not very often. I'd rather have a little denser bread without that cardboard taste of gluten flour.
Another thing you might try is mashing part of the grist, one of the steps used in producing beer. This converts the starches to sugars, giving the bread a sweeter more malty flavor. Mashing is used a lot in German and Russian rye breads. In addition to the flavor and texture it produces you get that nice shiny/malty sweet crust that you see on authentic German ryes. You can do this with any grain. The basic technique is to mix up the mash, which tends to be somewhat like a thick poolish, and put it in a 150-160 degreee oven in a sealed dish for about three hours. If your oven won't go down that far you can heat it to the minimum temp , turn off the oven and then put in the mash. You will have to turn on the oven at some point but that takes monitoring with a tHermometer Anyway the mash is added to the biga similar to a soaker, though the consistensies are different.
If you want really sour bread you really need to get the fermenting temp up to about 90 degrees but not much over that. You can take a picnic cooler and put a small lightbulb in it, keeping the lid cracked, to do this. I rigged up a thermostat designed for electric baseboard heaters. It works well becasue its designed for 120 or 240vac and has the relays built in