B-2 visa questions [closed]

Here's a little info about my situation:

Dutch citizen
Went on J-1 for 3 months in 2016
Went on ESTA in January for 2 weeks, in March for 4 days, and in April for 2.5 months in 2017
Have an American boyfriend in the US, who works for a North-American company
Not planning on getting married (have been together for under a year)
Applied for a B-2 visa to start around Sep 1th (paid fee, sent out DS-160, consulate appointment on August 24th)
Planning to stay less than 3 months, but would like to stay longer, but I've been in the US so much this year already
Last time I entered the border officer told me that he was "on the fence", but next time I would need a visa
Stupidly applied for a B-2, but my belief is that I can't cancel anymore
Planning on doing research for school (BA) during my stay while my boyfriend works
Need to be back to graduate beginning of next year at my university in the Netherlands and to have a planned mouth surgery
Have proof of funds of $10,000

Now these are my questions:

Would it be helpful to push the entry date to Oct or Nov 2017?
If I'm correct, I can't cancel my appointment anymore without getting an automatic decline for a visa, so not able to use ESTA anymore?
Are there people that have been in my situation that have advice for me or can tell me about their experience?
Does anyone know what my chances might be to getting a visa?

Thanks so much! I'm pretty nervous about the interview and I hope that this will help calm my nerves a little bit :)