1) I must preface by saying I havent done international but from what I hear CAL international isnt much different. Going out its still free jumpseat. Coming back to the US you pay taxes which range depending on where you are coming from. If you want to Non-rev (space available) you pay a fee based on destination and class you list for, but thats the same as domestic (just more expensive).
2) I dont have much info on other carriers international as I havent done it. Domestic....take your pick.
3) Immediate family (spouse, parents, a travel companion, kids etc) can list space available same as pilots on all CAL flights. Dont personally know and havent tried other carriers...
4) New hire reserve depends on base. CLE would be well over a year (maybe 2). I was hired in June and would have held a December relief line in EWR but not in IAH. That is only due to holidays... Likely 6-8 months to hold other than reserve in either EWR or IAH.
Hope this semi-helps...