Title tag keywords
 

I am working on my title tags. My main keyword is Odds Bonus (not an English website). I have a few questions I hope you can help me with:

1. I know I can't stuff the same keyword over and over again but it that also valid if the words are combined? E.g. "Odds Bonus, Odds Tips, Odds Competition"? Should I instead use "Odds Bonus, Tips, Competition"? I would like to rate high on e.g. Odds Tips and not just Tips but don't want to have problems with stuffing keywords.

2. Is it okay to use both the single and the plural version of my main keyword as well? E.g. Odds Bonus, Odds bonuses.

3. I know sentences are usually better but in this industry the users use single words more often than sentences so a list of keywords will work better for me, right?