Beatmatching by ear, two questions

Hi guys,

I very recently bought a Numark Pro to try a little bit of mixing because I am a big fan of electronic music. I believe I know the very basics by now, and I recently started to learn to beatmatch by ear. All I do is pure bedroom DJ'ing, I am not expecting anything out of it for now. It's pure for fun. Would love to have the skills to play in a club or so in the future, but for the moment it is just a hobby. I was wondering two things:

1. I am having a lot of problems to beatmatch two songs if they're having a different audio source (1 from cue headphones, 1 from monitors). Is it 'acceptable' / a good way to simply beatmatch with purely with headphones (both songs going through the headphones)? Or is it really crucial to learn to hear one song from monitors and one song from the headphones?
2. Beatmatching two 4x4 dance songs is going pretty good.. but sadly there are loads of songs with harder patterns and songs that are more noisy, is there any trick or there any easy tips to mix songs together?

I hope my questions aren't too newbish, this is just my first post here. It's all bedroom DJ'ing but I would love to get a solid start, that's also why I avoid the sync button. Other advise or beginner tips are welcome as well.

Cheers