Pretty much ready to book my flights except for one minor problem. Start in S America (nov - jan) and do se asia mar - may, or se asia nov-dec and s america mar-may?

Any advice would be really appreciated!
And tips on monthly budget for each place would be great as well - happy to do cheap sleeps and eats, but would like to do the Inca trail and some other excursions...

thanks!

The first option you mentioned would be preferable because that would enable you to catch the summer in S America. March to May is also a good time to visit the likes of Thailand because this is the end of the tourist season but the weather is still good.

As for excursions I would avoid the Inca Trail as this has become EXTREEMLY TOURISY in recent years and there is far better scenery and hikes to be done elsewhere in Peru like Huaraz for instance.