update keywords for existing site

Hey,
i was hoping to get some feedback advice, before i update my site

currently i rank #3 for "webdesign cityname" on my main/frontpage. I read lots about (on-page) seo and wanted to update my site.

i would like to rank my main/frontpage for "advertising agency cityname" and create two new pages for "webdesign cityname" and "seo cityname"

in the end i would want to rank #1 for "webdesign cityname"

• is this a good idea?
• will I lose ranking?
• do i need backlinks (deeplinks?) for the new pages?

i dont think the competition is that strong and i could build #1 worthy page/content but i have little experience with backlinks.

can someone give me an idea on what to do backlink wise? My idea was to use basic directory links on these two subpages?

thanks a lot