anyone that has been off milk products for a while is going to have a hard time going back onto milk. So do it very slowly if you are going to. Both of my children were lactose intolerant, not surprising because I am allergic to milk, not just lactose intolerant. I didn't know this until recently when I got allergy tested. But when both my children developed colic, which is just intolerance to dairy, I went off dairy completely because I was breast feeding. It solved their colic problems, and about 6 months later I slowly started putting dairy back into my diet. But I found that I never could ingest large amounts of milk, like a milk shake, without it giving me a stomach ache. When I was pregnant with my second child I developed gestational diabetes, which I found later was because I am actually allergic to wheat and dairy. and this caused me to develop type 1 diabetes even after I delivered because when you eat something you are allergic to, it attacks your pancreatic cells first. So the short of that long story is if you are going to reintroduce milk to them, do it slowly and carefully, just a tiny bit at a time, no more than a few tablespoons at a time. As for soy milk, be very careful with that too. Soy is the largest genetically modified crop so unless they drink organic soy milk, it is most likely GM, which carries a whole bunch of problems by itself. And on top of that, soy is high in estrogen, so not good to feed to our children very often, and yes, this also includes the beans. Rice milk, coconut milk (preservative free) and almond milk are better alternatives.
As for traveling, they will let you take it with you as long as it is for the baby. Call airlines ahead of time and find out individual restrictions.
Weaning from the bottle or from anything depends on the child. I would follow your instincts and see what works best for you. I slowly started introducing the cup and when they were used to it, just kept using it and made the bottles disappear. Once in a while for a crisis I would get it out, but mostly just offered the cup. I don't like to use plastic so I for the most part skipped those plastic sippy cups and went right to a small glass, shot glasses work well. Plastic baby bottles, sippy cups or anything plastic releases PBC's into their contents, so I found glass baby bottles on ebay. Good health to you :)