Osaka One Day Pass

What does OTS line stands for?

I'll be using the Midousuji Line, Sakaisuji Line and Tanimachi Subway for one whole day, is this the correct pass?

To sidetrack, nearest station to Den Den Town is Ebisucho?

What does OTS line stands for?

大阪港トランスポートシステム or Osaka Port Transport System. It is the last short section of the Chuo Subway Line between Osakako Station and Cosmsosquare Station:
http://www.japan-guide.com/e/e4010.html

I'll be using the Midousuji Line, Sakaisuji Line and Tanimachi Subway for one whole day, is this the correct pass?

The Osaka 1-day pass for subways will probably be a convenient ticket. And if you use subways a lot, it might even pay off.

To sidetrack, nearest station to Den Den Town is Ebisucho?

Yes. Nipponbashi is also reasonably close.

By all means go to Den Den town but the stores are small and crowded so it is hard to really look at the stuff.
Bic Cameras in Namba http://www.osaka-info.jp/en/search/detail/shopping_5137.html

and Yodobashi Cameras http://www.swiftcity.com/guides/japan/54/474.html
are more practical places. And you can always find staff that speak English.

Despite their name they sell way more than cameras, TVs, computers etc. they also sell all sorts of stuff that use electronics in one way or another..from refrigerators (quite different from western style ones) to automatic toilets to remote controlled ceiling lights to...you name it ...

Thanks for the clarification! I could just buy the pass from the ticketing machine? Is it easy to navigate? Any option I need to look out for?

Uhhh, I wanna go to den den town as both me and my bf would like to check out the gundams and other anime/games collectibles.. We aren't there for electrical stuff as we can get it at akihabara too.

I will be having one full day in Osaka, reaching about 11am and leaving 7am the next morning. Other than dotunbori and den den town, what other interesting sights I can check out.

I could just buy the pass from the ticketing machine?

Yes,

Is it easy to navigate?

Yes. But if you run into troubles, you can ask the station staff for assistance.

I will be having one full day in Osaka, reaching about 11am and leaving 7am the next morning. Other than dotunbori and den den town, what other interesting sights I can check out.

Some other sights:
http://www.japan-guide.com/e/e2157.html