Pursuant to legal ethics rules, this does not constitute legal advice, it is for the purposes of discussion only. Accordingly, consult a licensed attorney before relying on any of the information below:
(1) Typically an SEC filing is necessary when an investor invests pursuant to rules 504, 505 and 506 of the 34' Securities Act. A way to not have to file, right away, is to do a convertible note where the "investment" is a loan that's triggered into equity at some point in the future. At the time equity is "triggered," this would probably require a filing.
(2) This relates to your first question. A VC investment would be governed, most likely, under rule 504, 505 or 506, depending on how a deal is structured. Another thing to keep in mind is compensating a third party for helping get an investment. This would be considered a "promoter," which is not legal under securities laws. Only broker dealers (investment banks) can get a percentage of a fundraise. You would have to have proper structure in this instance.
(3) One thing to keep in mind is the requirement of an accredited investor in 506. An accredited investor is someone who has certain earnings per year or savings that meet statutory requirements. It is possible to have an unaccredited investor, but, in this instance, this investor would have to be "sophisticated" and the issuing company would have heightened disclosure requirements (typically in the form of a private placement memorandum). Also, there are certain due diligence requirements that companies may need to meet depending on which Rule they use. Finally, there are, in some cases, state securities laws that companies need to be cognizant of.
Happy to talk more. I do a lot of work in the tech/fundraising/securities legal spaces, and have a tech company of my own.