Under normal circumstances, the best option for you is to apply for a single K1 visa only even if it is possible to apply for more than one. Citizens of Argentina, Australia, Austria, Canada, Chile, Denmark, France, Germany, Hong Kong, Hungary, Iceland, Ireland, New Zealand, Norway, Poland, Portugal, Republic of Korea, Slovakia, Spain, Taiwan, and the UK are all eligible to apply for a working holiday visa to Japan.
A visa number retrogression means that EB1, EB2 or EB3 applicants from certain high-immigration countries will not be able to apply for an immigrant visa (by filing an I-485 or through Consular processing) until a visa number becomes available for their priority date.
If you do not meet the above criteria, for example if you want to pursue Bachelor studies, or are applying for preparatory classes (also language classes) with the intent of entering a German University later, you have to submit your application directly at the competent German Mission.
Beware of unauthorized private websites that offer ESTA application assistance for $49.99 – they are usually not authorized to practice immigration law and are asking travelers to pay for a copy of the application questions, which are free on the website.
Re-entering the USA after a full ninety (90) day stay and brief departure is not strictly prohibited, but the officer may deny your entry based on suspicions that you intend to permanently reside in the United States, will not leave by the expiration date on your I-94, or that you are engaging in unauthorized work while in the United States.