Nepal - indonesia travel question

the situation:

after graduation in summer (master degree), me and a good buddy have decided to do a month long trip to asia in end of september/beginning of october (were from europe, austria). i had the idea of going to nepal doing some trekking and together we thought it would be cool to finish the trip on a few of those chill indonesian islands for a few days (i know its still a 6-8 hours flight, but a lot closer than from here)


so basically, has anyone (who has been there obviously) legit infos, especially on these topics

1) tips on cheap (national) flights (yeah, the internet) in the area (india/nepal/thailand/indonesia/...)

2) how serious is this whole acclimation thing? like usually people say to go from lukla to everest base camp for example, you should "need" around 9 days or so, for a 30 something miles hike with around 7000 ft vertical difference. i know its not a cakewalk in that altitude, but we both live in the alps and regularly are around the level of lukla i would say when doing stuff in the mountains and are generally not unfit. this means that we both could do this in one day if the "goal" was at 9000 ft or so.

3) related to 3, if you only had 12-13 days to trek do see as much of this wonderful mountains, how would you set it up?

4) fun stuff/islands to visit in indonesia. basically anything, some beginner surf stuff, or anything adventorous. i know bali is pretty famous for such low budget travels, but maybe someone knows something else.

5) or even anything else that is worth a visit in the general area, like in thailand/laos/cambodia/vietnam/malaysia or so




thanks a lot guys for any info, really appreciating anything. i will also bump this shit notoriously over the next few months.