Unless you've already bought ticket, my suggestion is to avoid Jetstar, if possible. There are number of reports of canceled flights. Generic rule applicable to Jetstar is to avoid the first and last flight.
Another thing is that with most LCC (AirAsia is exception) you can't get boarding pass even if you have no checked luggage. You need to stop at their checkin counters and do checkin/document verification. You can't do it on airside, only on landside.