You may want to consult a lawyer. My opinion is that you should wait till you come back from the conference before submitting your petition. I may not be right though.

The earlier you file the better. Filing for an i-140 raises questions when you get back, if the visa is not current you cannot do consular processing you have to wait for it to be current.

Since you still are on F1, you don't want to raise an immigrant intent flag. I will say wait until you are back from your conference before you submit. If you submit now, there is a high chance you will be flagged for immigrant intent when returning which may or may not lead to being denied entry. I will say don't take the chance.

I have heard some filed I-140 and travelled. As a matter of fact, they went for their F-1 renewal. while away, their (three of them) I-140 was approved. They also got the F-1 renewed and got back successfully. I also have heard of people who went out and couldn’t get back due to raising immigration intent. I will suggest you contact a lawyer

I was in a similar situation, however while being on a J-1. I had an approved I-140 at that time and was told by my lawyer that I would have a very high chance of not being admitted at the border. Even submission of an I-140 shows immigrant intent. I ended up canceling my trip. I heard that a friends lawyer gave similar advice, however that was also J-1. Hope this helps.

I don’t see any problem with filling I-140 and traveling. the issue comes when filling AOS (i-485), that’s aftey approval of your 140 (NIW). that being said you may want to avoid any risk and cancel any travel until you got a trave document (advance parole) following your AOS application