Why a separate VCR for cleaning tapes? It’s enough to clean the heads AFAIK.
Also, you should definitely not use default deinterlacing techniques for the video, especially not ones built into these generic dongles. Capture it interlaced, preferrably as losslessly as possible, then use deinterlacing software where you can fine-tune the settings if you need to.
No, TBC most likely cannot be done in software, unless the video features a prominent vertical bar (such as a black border). It depends on the quality you want to reach, look closely and decide if the jitter is acceptable.
Edit: TBC can obviously be done in software if you have the raw composite or head signal but that is not possible with the capture cards you have.