Tough to say - when fina first came out (long before kits - like early 90's and no one used it much) I did 2 cycles where I crushed up 3 tabs per day, heated them in 1-1.5 cc of oil over a stove to make solution, drew into syringe, let cool, and injected. No infections - no pain - excellent results. Does that mean it was sterile or that I would be comfortable doing it today. No.
You are mixing your injectibles together (different kinds?) - I can't say this is good. This is why sust 250 only comes in 1cc amps. If it came in a larger bottle it would not retain consistent proportions for each injection. Each ester has a different structure and weight. The active swirling before pulling it into a syringe might help but there is just no way it's going to be 100% even.
Also the boiling point of BA is relatively high - I'm not convinced that this works at removing BA (unless the manufacturer is not using BA but a more volatile alcohol with a lower boiling point - is this IP stuff? This is what I noticed when I heated his. Perhaps this is the cause for the painful injections and lumps - not BA? Who knows but I'm not the only one who found it curious.)
For bacteria purposes I would go with the method of bringing it up and down to temp around 3 times then apply the filter.
Reheating the syringe is just an attempt to lessen the viscocity (spelling?) and make the injection less painful as the oil should spread easier.
This is a lot of trouble to go through. Obviously you don't trust the person who's making your gear. I'd think on that for a while. Personally, I'd buy higher quality. Smooth painless injections and no bullshit.