I'm planning to go Odaiba after taking the Shinkansen back from Odawara.

Estimated time of arrival at Tokyo station is 5:30pm - 6pm. Might be earlier.

I saw from the website that Odaiba can be reached by boat from Asakusa, however, I seen the web page and the timing are all quite early.

Would any kind souls please advise how should I go about doing it if I want to take the boat to Odaiba and take train back to our hotel at asakusa..?or vice versa?

Upon reaching Tokyo Teleport station, is all the attractions walkable distance?

I'm only looking at:
1) Decks Tokyo Beach
2) Fuji Tv
3) Palette Town

and if theres time
4) Tokyo Big Sight

There are boats from Hinode Pier to Odaiba, but Hinode Pier is not so easily accessible. And the boats might not be running anymore depending on the day of travel. They run longest on summer holiday weekends.

Alternatively, you can go there by Yurikamome or Rinkai Line, as explained on the following page:
http://www.japan-guide.com/e/e3008.html

Upon reaching Tokyo Teleport station, is all the attractions walkable distance?

Tokyo Big Site seems to have maps of Odaiba on its website, which may be a good help.
- Tokyo Big Site: Page for access maps
http://www.bigsight.jp/english/general/access/index.htm...
- Tokyo Big Site: Color access map (PDF file)
http://www.bigsight.jp/download/public/access_map_e_col...
- Tokyo Big Site: Monochrome access map (PDF file)
http://www.bigsight.jp/download/public/access_map_e_mon...

: I'm planning to go Odaiba after taking the Shinkansen back from Odawara.
: I can only take train to and fro from Tokyo?

Your Shinkansen train will reach Shinagawa Sta. about 10 minutes before Tokyo Sta.
When you don't have heavy baggage, I think this route will be more time-saving:
Shinagawa Sta. - Osaki Sta. - Tokyo Teleport Sta. on (non-JR) Rinkai Line.
The required time depends on crowdedness in the stations, but I estimate it as 20 to 30 minutes.
(After Step 3, using coin lockers on the concourse might be your option.)
1. Exit Shinkansen through Shinkansen North / South Ticket Gate (not Transfer Gate) to a passageway in Shinagawa Sta.
2. Ask a station attendant how to buy a ticket to Tokyo Teleport Sta. of Odaiba.
3. With the ticket, enter JR-East through Central Gate, which is along the passageway.
4. Take a train (at Track 2) on Yamanote Line's outer loop for Shibuya and Shinjuku.
5. Osaki Sta. is the next station; get off your train there.
6. Change platforms to take a Rinkai Line train, which may use Track 5 / 6 / 7 / 8, and get off at Tokyo Teleport Sta.

: take train back to our hotel at asakusa..?

If your hotel is easily accessible
from Asakusabashi Sta. (of JR-East / Toei subway) or another station on subway Toei Asakusa Line,
then how about taking a Yurikamome train to Shimbashi (via Rainbow Bridge) and making a transfer to Toei Asakusa Line?
Maybe a better railroad route exists if yet another station is most convenient for your hotel.

//