Going to Shikoku question

I heard Shikoku is a good place to visit esp. for seafood.
I plan to visit Takamatsu (Kagawa)for the sanuki udon and maybe the Ritsurin Koen. I also plan to visit Matsuyama (Ehime) for the Dogo Onsen.
Anything else worthwhile to visit in Shikoku? I like seafood, any suggestions?
Would daytrips from Okayama suffice?

More information about what to see on Shikoku:
http://www.japan-guide.com/list/e1107.html

Kochi is also a pleasant city, famous for katsuo no tataki:
http://www.japan-guide.com/e/e5606.html

Would daytrips from Okayama suffice?

Train travel on Shikoku is rather slow. A round trip from Okayama to Matsuyama, for example, takes almost 6 hours. Kochi is similarly distant. Only Takamatsu is accessed more quickly.

Also, Dogo Onsen is best enjoyed by staying overnight.

Hi
I also remmend you Kochi!
I went Shikoku almost 10 years ago. First I went to Ehime. I took a local taxi, and talked about sightseeing spots. He said, ''When you come to Shikoku, Kochi is a must. '' So, Ichanged my original plan and went to Kochi. I went sunday market in downtown. It is very interesting There are a lot of venders along main streets. People are very friendly. I was treated by local woman. She took me to small area where we ate local seafoods.

Uji,
I think Okayama to Matsuyama is 2.5 hours away JR Rail Pass, not 6 hours.

Right. Therefore, the round trip would be 5-6 hours.

I am coming from Himeji.
I want to visit Takamatsu, Matsuyama, Kochi. Because travel time for these cities are at least 2 hours one way. Would it be advisable to stay overnight in each city? What order of city or route should I take?

Also, are LTD. Express Trains commuter trains? Are the chairs like Shinkansen or Hikari?

The Limited Express is a regular express train with regular seating (seats that rotate but do not recline). A green car is available, but I've never been in it, so I can't vouch for its seating quality.

Would it be advisable to stay overnight in each city?

Yes.

What order of city or route should I take?

It does not matter. Any order would be fine.

Also, are LTD. Express Trains commuter trains?

"Limited express" is a train category. It means that it skips a lot of the smaller stations. Some people use limited express trains to commute. Some people even use shinkansen trains to commute. Most people on the Shikoku limited express trains are not commuters, though. Train categories are explained in more details here:
http://www.japan-guide.com/e/e2016.html

Are the chairs like Shinkansen or Hikari?

Yes, very similar. Some recline. Some don't. It depends on the train set. There are usually 4 seats per row.