Arriving SIN on UA 1 from SFO at 6:15 am. I have a choice of a few LCC to get to SGN. Thinking about Jet Star for Price and have a few questions..

How do you transfer from UA Arrival to Jet Star (can you stay in the sterile area and not go through formalities when changing terminals)? And the time involved. Only transferred SIN once and stayed in the same terminal..

Last time I went to SGN I took SQ and the price is quite high now compared to Jet Star.

If you can stay in the sterile area do Jet Star check carry on weight at the gate. I have a complient carry on in size and would be over the 7kg allowance.. Normally it's not an issue with other carriers but with Jet Star I thought I would ask.

And what about Scoot as well (they ask for a SQ Frequent Flyer # are they some way associated?

I'm traveling with my 20 y/o Son and don't want to mess up (he looks up to me as a FTer)

Thanks in advance..