I've not heard of the Jade Buddha, but yes, the rest is possible for two days.
I think you will hit all the HCMC sites on the first day and Cu Chi Tunnels the next day. The first day in HCMC you will probably want to arrange your tunnel tour.

I would recommend drinking some local beer (I'm assuming that you live in BKK). I like the Hoa Vien microbrewery.

I think they might have Mekong Delta day trips, but I wouldn't want to have to catch a flight that same night.

If possible, stay longer.