Q1... between Wordpress and Blogger? Wordpress all the way... But there might be blogging platforms that are better than WP, I don't know cause I've only used WP for the last 10+ years
Q2... what does this question mean? I don't understand it unfortunately
Q3... personally, I don't like KGR, but some people swear by it, so I don't know what to tell you except for the fact that if you're good at keyword research you're gonna spot easy keywords no matter if they're KGR or not. But since you're newbie at SEO focusing on KGR is probably a good idea until you get the hang of keyword research. But even if you find 1000s of good KGR keywords that doesn't mean you're gonna rank for them, because a lot of other things are at play when ranking, KGR alone doesn't cut it anymore. You need to get everything else about your site spot-on to please google. KGR keywords don't just rank on their own without you doing on-page SEO and sometimes even off-page SEO (backlinks)
Q4... of course that not all KGR keywords rank since google doesn't favor page titles hugely like they used to do when the KGR method had come out. But the fact that your keyword didn't rank could be attributed to many things, some of which include:
- your site's poor structure
- your page's poor / non-existent on-page SEO
- your site's sandbox (if any)
- your niche (niches like banking, travel, health & fitness, SEO, web hosting, insurance, education, medical conditions, ecom and 1000s others are very competitive, in general, and new sites won't break into these niches with just 1 article and no domain authority)
- tough competition for your KGR keyword
- etc...