I strongly considered deleting your question without comment as it has been answer innumerable times in the past. Instead, I will provide a brief answer with no follow-ups. If you wish for more information search the archives of this site.
The scientific data from observation of not thousands but truly millions of exposures is that HIV have NEVER been transmitted by masturbation of an HIV infected sex partner, This is irrespective of the presence of peeled skin, cuts, hang nails, rashes, etc - still never. You are not going to be the first and for you to even be concerned is unfounded. Similarly, testing is a waste of time and money.
With respect you your questions:
1. There are many layers to the skin. When there is trauma such as a cut or scrape healing begins immediately. Thus, no risk.
2. This is a theoretical question for which there is no scientific answer. The body does not use a single host defense mechanism to fight HIV but many. In combination, this translates to no HIV transmission through masturbation, even in the unlikely circumstance that your partner had HIV.
3. ???
4. Again, not a question that makes a whole lot of sense. Please remember that when HIV has been spread by non-sexual ways, it is injected into the blood stream, not simply splashed or otherwise applied.
This ends this response. There will be no further answers. EWH