If you get married within 90 days, you can adjust today, tomorrow, or even 10 years from now despite overstaying the K1. You just need to file your I-485. Since you married within 90 days (while the K1 was valid), you've got no worries. If you'd like more info about the process, here's a useful do-it-yourself video guide (always best to hire an attorney, however): http://westimmigration.com/standalone-i-485-adjustment-applications/
It's actually not a cut and dried answer to your question. If the person has used the visit visa in the past, and on this particular trip, just gets waived in without much questioning (as is often the case), it should be ok to apply for adjustment of status with an I-130 petition (212a6ci shouldn't be found under those circumstances). This is a very fact-specific issue, and it's best to speak with an immigration attorney about this and to have an attorney attend the interview (I've help clients...
If it's excessive, contact USCIS and do a service request, and they should promise action within a span of time, and if they still delay, you can contact an AILA member attorney who can to a liaison inquiry.
Also, if you are called for a second interview, it would be a good idea to have notes of what you said in your first interview so that you will be sure you will stay consistent. The attorney is the only one who can appropriately attend the interview with you and take notes for you.
Yes, assuming you have an EAD (or if you're in H1B status, you can file a change of employer petition, assuming you have recent paystubs at the time of filing). The priority date for EB3 is far off, but you should find a substantially comprable position (meaning the job duties are at least 50% the same), and should inform USCIS that you have ported your employment with an AC21 notice letter as soon as possible. This will preserve your GC sponsorship pursuant to AC21 regulations. Self-employment...
If she marries you, then the process is relatively straightforward to file an immediate relative petition along with an I-485. If not, then you'd better not overstay and leave after being out of status for 6+ months, or else you'll trigger a 3-year bar of inadmissibility.
You may click the link below to find some useful free attorney-prepared self-assessment tools relating to these cases.
In response to the additional information, if there are no lapses in wage, then there should be no problem in extending your H1B UNLESS the employer is H1B dependent/willful violator/TARP recipient AND that you are not an "exempt" H1B nonimmigrant (meaning you have a masters or at least a $60K salary) AND the employer displaced (laid off) an essentially equivalent US worker (one whose job responsibilities are essentially the same as yours) within 90 days of filing your LCA (which is required in...