Personnaly i have no idea about most of these things, but there's one question i can answer to.

You can use any language you want, personnaly i'm french but i use english because i think it's better for the viewers and stuff. Just use what you like / want, just keep in mind that not everyone can understand that language, so you should expect peoples to ask a question at some point (nothing bad at all, it keeps the chat / game active in a way).

timer program is something like wsplit, seperate program you capture with OBS, download it (there are a few options on he resource page http://www.speedrun.com/resources ).

if you add your twitch to the profile, you will show up on the stream page (unless there are bugs again).

rules is a hard question, someone else can help.

when you recorded your run, you make a highlight of it (or export to youtube, or local record and upload to some site that you have a link). if the game exists on the site you can submit the run at the game page at the right top. if the game is not on the site (and has no other leaderboards community, if there is talk to them first and get them to move maybe if they want) you can request the game at the games page, again right top which will take you to http://www.speedrun.com/requestgame where you can request it.