Welcome to the forum. Thanks for your question.
I would encourage you to not worry at all about STDs or HIV from these events. They were completely risk free. With rare exceptions, STDs require penetration for transmission. The bacteria and viruses that cause them are not simply infections that happen to primarily involve the genitals. These organisms evolved to require penetration for transmission. In addition, saliva or oral contact is rarely a source of infection. Among other things, saliva kills HIV and also is toxic to most STD bacteria and viruses. Further, these organisms cannot be transmitted through clothing materials; the cloth fibers would effectively filter them out, at least to numbers that are not infectious. While nobody can say that such exposures are truly risk free, the overall chance of any infection is so low that it can and should be ignored. In my 40+ years in the STD business, I have never seen nor even heard of any patient who acquired any STD or HIV from exposures like yours.
Those comments pretty well cover your specific questions. But to be explicit, so there is no misunderstanding:
1) No significant risk. In addition to the above comments, contact of infected fluids with intact penile skin is not a risk. (The skin of the penis is no more susceptible to STDs than skin anywhere on the body.)
2) It seems pointless to speculate on potential exposures that almost certainly didn't happen. But this still would be very low risk: genital apposition, without penetration, is very low risk.
3) Even if her personal hygiene is as you describe, any semen from previous clients would be too small in amount, and would have dried sufficiently, that transmission of STDs would not occur.
4) STDs are never transmitted by contact with linens, towels, etc. No risk at all.
5) Use of lots of lotion does not increase risk. In fact, it probably reduces it: a) Many (most? nearly all?) lotions contain anti-infective preservatives or are otherwise toxic to bacteria and viruses. b) Improved lubrication probably reduces the kinds of contact that could transmit some STD organisms, i.e. less chance of microscopic abrasions.
So as I said above, you really needn't be worried at all. You don't need any STD testing and if you have a regular partner, you can safely continue your normal sexual practices without risk of transmitting any STD from this even. Of course you are free to be tested for common STDs anyway, if the negative results would further reassure you. If so, have a urine gonorrhea/chlamydia test any time more than 4-5 days after the exposure and blood tests for HIV and syphilis after 6 weeks. (This does not mean I believe you are really at risk. I do not.)
I hope these comments are helpful. Let me know if anything isn't clear.