Potential itinerary during TET & advice re travelling around

Hi,

I have been trying to get this answer by reading the posts, my lonely planet etc but am slightly going into panic mode because of what I am reading so thought it would be better to ask a direct question.

I arrive in HMC on 2nd Feb & am spending few days around there doing the usual tourist things & culture.
Overnight train booked to Nga Trang on 5th Feb
6th to 10th thinking of hiring a motorbike & doing the Nga Trang, Dalat & mue Nei triangle as I heard it is beautiful & I am a very experienced rider.

This is all with a friend & then I go it alone.

I would really like to head to Cat Thien Park is this easy to get to by bus from this area? & worth the hassle? If it is an hassle I am thinking of headin to Hoi An instead. Advice on how to get to either of these during this TET period much appreciated :O)
I then want to go to Pho Quoc Island (maybe via Mekong Delta if it easy enough to do via buses from Central Vietnam or central highlands so any advice much appreciated?) or the other option is to fly. I see it is easy to fly there from HMC but its a pain to head back there & then fly out again. So advice on any alternative way to fly much appreciated or travel overland or boat much appreciated

I was then planning on flying back to HMC on 18th as fly back to UK last thing on 19th.

So really the advice I need is;
Does the transport run every day over the TET period? Do I have to book everything in advance? I know prob trains & Planes is a defo yes but what about open tour buses or the local bus service?and if I need to book open tour how do i do this from UK?or can I do it when I arrive in HMC?
Can I book Air Mekong & Vietnam internal flights from here in UK? as those are 2 options to fly from Pho Quoc to HMC.
If I dont go to Cat Thien Park, woudl anyone suggest any other rainforest/national park to visit with easy access as I do love a rainforest :O)
Will I need to book accomadation during this period. I was planning on booking HMC & the first night in Nga Trang but then going with flow like I usually do when I travel?

Any advice much appreaciated, as I am slightly starting to panic :)

Cheers