Two questions!

[Silverthorn]

Hi, welcome to LFE!

And if i get money with the mod(i dunno how hahahaha, just asking for future plans), how much i'll have to pay for the main characters owners and lf2 original owners?

Making profit off of LF2 might be difficult. Not that your potential target group (people that want to play something Little Fightery + willing to spend money) might be fairly slim, you'll actually have some juristical obstacles as well. Let me quote from the EULA of LF2v2.0a:

3. Restrictions

You agree not to modify, adapt, reverse engineer, decompile, disassemble or otherwise attempt to discover the source code of the Software. You are not allowed to sell, re-sell, rent or lease the Software, any portions of it or its license or any portions of a license without written permission from the Author. You are not allowed to remove any product identification, copyright, proprietary notices or labels from the Software.

Now, here comes the crux: the Author is Marti Wong; he, however, has sold the rights of LF2 to U1 Technology, a game-company that is most notably known for the release of Little Fighter Online. Don't even attempt to look it up, the official LFO-website has been taken over by some crackpots that now tell you that you won iPhones galore. In short: the licence and usage conditions have gotten way too complex for anyone to keep track of. I strongly recommend you to not sell anything, then you should be fine.

2- If i wanna make the mod with a online server(not sure about that yet, just asking for possible future plans too), how does it works?

That solely depends on what that server is supposed to be capable of! What have you planned that you would need it in first place?