Whenever you make clabber, it's a gamble for what you wind up with as the first generation, and also a gamble for what you achieve after a few generations. Clabber is not some magical answer to everything and it's not a given that just because you let milk sit out, it will form the most beautiful, thick, tasty lactic curd. More often than not, the opposite happens and you wind up with something weird, or slimy, or with off flavors and smells. Don't despair, it's all part of the process. Unless you plate out your milk and isolate colonies of everything that grows, it is tough to get it going right away. Think of it like this. There are all sorts of bacteria, yeasts, and molds everywhere. Many of them like very similar conditions for temperature and food. When you put all of them together, it forms a soup of all sorts of stuff. The way to try and isolate them if you're not banking them is to try and let the strains you want dominate. So you create favorable conditions for those strains.
For example, say you were making thermophilic clabber and are trying to isolate a starter for mozzarella or for many Italian cheeses. What you would do there is thermize the milk to 125-130F or so, and then keep the temp at 105F and let it sit out to see what happens. The thermization would kill of mesophiles and psychotrophs, and then the constant temperature (vital) of 105F would encourage bacilli and S thermophilus to grow.
Or if you wanted to make mesophilic clabber, it's a similar process, but it's harder because you have to keep the temps around 88F, and at those temps, many other things will grow. One way to mitigate this, is to try and isolate more active meso bacteria, such as L lactis and L cremoris. Both of those will grow at 100F. And at 100F, you are at the high end for leuconostocs, yeasts, etc, which will be inhibited. So that's one approach, to control the ratio through temperature, and then keep propagating forward with the higher temperature until the ratios of the various participants in the biological ecosystem shift over to only lactic bacteria.
Another approach is to keep the temp more moderate, such as at 90F, and keep culturing forward, and let the natural bacteriocidal compounds that lactic bacteria produce cause a condition where the lactic bacteria predominate. This is really tough because it's a roll of the dice for what bacteria you have in your environment. From your last batch, you had a really, really low load of lactic bacteria. Not too encouraging. But your process was inexact. Leaving milk out to sour, while romantic, will not help you get to where you want because starter culture science is really precise. Once every great while someone somewhere can achieve good clabber at room temp, if they have a high load of leuconostocs, but that's very regional, and rarely happens overall.
If you add buttermilk to clabber, IMHO, I don't see the point. You're contaminating the buttermilk at that point, because your clabber is not stable. It will help you shortcut through a few propagations, but it will not give you a stable, multi-generational, strong starter.
to sum:
- it is vital that you can control temps very exactly, if you want repeatability
- usually takes many attempts to get anywhere
- It would help you tremendously if you understood the basics of how microbiological communities work