1) Yes there will be less nausea if you take your dex after a meal, but it will also be weaker(and the DXM content will be higher than the DXO). I usually dose on an empty stomach. Weed is always good with DXM, so save some and smoke it when you get the nausea from DXM. Dramamine also helps(no more than 50mg is needed), but that will increase your DXM/DXO ratio.
2)Nope, to get the most DXO, you will need to dose on an empty stomach(some toast to ease nausea is fine and is recommended), preferablly DXM HBr or agent lemon, free base will take a while to be absorbed and will also be a lil more harsh on the stomach. Dose all at once and drink gf juice the day before and on the day of the trip. Drink it at least 4 hours before your trip. GF juice will definetly help, but it's not to important(I never do, tastes nasty). Also you should avoid all medications that are CYP2D6 substrates/inhibitors if you want a DXO trip. A common example of a 2D6 inhibitor is CPM, a common substrate being dramamine(forgot the chemical name, something similar to diphenhydramine).
3)Not sure about that there, DXM is so powerful nobody really has a definitive answer. But I would assume most dissociatives share similar effects. DXM makes me very rational, like I would say stuff normally I wouldnt say. Makes me more social because it dampers my emotions down a lot(anxiety being one of them). Also gives me incredible amounts of engergy, one of my friends always falls asleep on DXM, I can never figure out why...
The last question about ego is a bit hard to answer because everyone is different. We might be talking about similar effects but we have no way of comparing them. Ego death is what comes with most high dose psychedelic & dissociative trips, be prepared. Noobs always say theyr prepared for that first 3rd plateau dose, Hah, I laugh inside when I heared my friend say that(he tripped his ass off and now gives DXM the respect it deserves).
Peace out, trip safe