The viral inoculation load is a key gap in our knowledge base for testing and policy. I struggle with test interpretation not knowing at what level a test should be positive since the question is not if the virus is present but rather: A. if the illness is caused by COVID-19 and if the person is infectious. Something I think about daily.
It probably has to do with testing how much passes through the mask. Then you know what viral load you need to get infected. That probably has a probability curve. So you can then look at that probability curve and find a percent chance of catching the virus.
Touching your mask will have minimal effect. the Virus is rarely transferred by surface contact. Cleaning and washing hands help but is not the major mitigation, masks and social distance are.
Wearing masks is the first thing, next is wearing an effective mask (neck gators don't work well, nor do bandanas or single layer cloth masks)
The virus as a particle is extremely small (0.1 micron) but that is not the concern. The concern is droplets which are 1-10 microns. Most of the droplets are captured by masks. Face shields protect the wearer to some degree but have minimal benefit for everyone else, similar to the valve masks.
One study I read had transmission between a known infected person and unaffected without masks <6' for 15 min without masks at 17%, if the affected person is masked it was 3% and if both were masked it was 0.5%. Not sure how those numbers were calculated. But as you point out, a properly fit mask makes a big difference.
In the US vaccine distribution is likely to be a state by state process. Most experts agree that distributing the vaccine to front line health care workers is 1st priority to support the medical care system. Many agree that essential workers should be next followed by at risk individuals and finally healthy adults. But there are a ton of possible paths.