Hi i think you can get many position but only in long tail keywords . In short keywords their is lot of competition dn all webmaster try their best to acquire those places .
Possible you need to have 100 backlinks for anchor text A another 100 backlinks for anchor text B another 100 backlinks for anchor text C .....etc
Hi For First Que You can rank #1 for as many keywords you want but for that you will require more back link and quality of links.. Second - If you are getting links from your main keywords along with other keywords then it wont affect much to your rankings. Yes,Quality of link is important.