Hi Maj
When you do give the bottle occasionally, start off with only 60mls & see if she wants more after that. Unfinished bm can be given once more later on but then needs to be chucked away.
You can express milk & store it at the back of the fridge for about 5-8 days! If you know you not gonna use it in those days, rather freeze it.
Regarding the teat. You get the smallest one & stick with it.
With regards to the tugging. You can maybe try breast compression to see if it helps OR just offer the other side.
www.breastfeedinginc.ca/content.php?pagename=doc-BC
Also,
As she starts to get full, she may pull away only to decide that she would like a bit more milk after all. In this case, let her show you when she’s truly through eating. Help her latch back onto the breast to see if she continues eating. If she pulls away again and seems content and calm, consider the feeding done and move on to burping her.
Bringing up milk is quite normal. The milk some times lie on top of a wind & when she burps it get brought up. It doesn't really sound like she suffers from reflux cause she is gaining well & seems quite happy overall.
Remember that your milk supply gets established around 6weeks & your breasts will become softer later on & won't feel "full" & firm anymore. It's perfectly normal because your milk doesn't get stored in your breasts

So don't panic once that happens.
Does she hurt you when she feeds?
The trick is that she needs to open wide when taking in the nipple & areola(not the whole part). Tummy to tummy! Tickle her upper lip with your nipple until she opens wide enough & then bring her in quickly towards the breast. Lips curled out like a fish