1) You don't have to write like a news editor, copywriter or journalist. Some of the most popular blogs are just real people talking in slang, sometimes getting mad and sometimes being funny.
One blog in our industry that comes to mind that has a HUGE following is Shoemoney. He admits he has ADD, jumps all over and can't spell. Doesn't matter, people love his personality and the info he shares.
Soooo don't worry about perfection HOWEVER if you write about something you know about OR are passionate about OR are excited to learn about then it's easier for you to let your personality shine through.
2) Hard to say. Depends how good you are.
PLUS you don't want to only look at how popular the KW is, but how competitive, so you need to eval both numbers.
There is no hard and fast rule so I'll just throw out some numbers. I use
affiliate marketing as my oversaturated benchmark, because I already do PPC for 5 Star and know how competitive this space is.
SEObook Wortracker count:
768 (Popularity)
Google allintitle: "affiliate marketing"
825,000 (Competition)
BAD oddS - HORRIBLE numbers! (Why do I even try to do PPC in this market. Google Adwords even told me it's too competitive for Adwords to be very effective.
My low bench mark as far as just knowing this would be a fairly easy ratio for a fairly skilled person to target is:
SEObook Wortracker count:
800 (Popularity)
Google allintitle: "key phrase"
5,000 (Competition) (my secret low competition phrase I've never done anything with.)
NOTE: So using the above you have a range of RATIOS you could use for any numbers in-between. But there are still other variables to look at before deciding on a niche that depend on other factors. These numbers would just be initial screening to see if a niche has potential.
Now since I used to do
SEO for a living I'd tackle something much more competitive than 5,000. If I were a newbie I would probably try to stay under 2,000. If I didn't care about making big money right away but wanted a good easy market that I could learn in and feel some fast success I would look for a ratio of around. 200 popularity vs less than 100 competing. (totally guessing at those numbers and they could vary a lot depending on your situation.
2 OTHER IMPORTANT THINGS TO LOOK AT!
1) Who's on top in the search engines? Even if it's a low competition phrase, if all the top sites in Google are news sites and well established authority sites, it would be hard to crack for a newbie.
2) How would you monetize? Are there products that people looking for that key phrase would be looking for? Do those products have an affiliate program? One good thing to look at: do your keyword search in G with no quotes or allintitle. Check out the Adwords ads to see how many are promoting something and what THEY are selling.
NOW based on the potential niches you mentioned I found a hot one for you. Hot in # of searches VS hardly any competition. NOT HOT as far as monetizing the niche.
So if you were interested in pursuing a niche that would be hot right now, has growing interest, something you are interested in learning more about, would enjoy blogging about, would be easy for you to learn and see some early success, but may not make you much money, let me know and I'll tell you by PM so I don't give the niche away and create competition for you.
If you don't want to start off with a hot easy niche, but really need to make money fast, then I'd give this niche away here and use it as an example.
Let me know if you want to know the niche so you can decide.

Then I'll tell you the niche in private, but post the general details publicly so everyone can learn in the process.