What is the key factor to increase blog traffic?

Those are good questions, but remember to keep something in mind:

Effort does not equal reward.

One marketer can put in 1 hour a day and earn $10,000 from his efforts. Another marketer can put in 18 hours a day and earn a big fat zero.

One of of the biggest newbie mistakes (no offence; we were all newbies once) is to put your heart and soul into a blog and assume Google will deliver.

In that scenario, the cold hard truth is that Google will almost never deliver; not unless you know what you're doing with content, design, and SEO.

The best help I can offer, in the time I have this afternoon, is to look at your blog (I haven't seen it) and understand that it probably needs a redesign. Second up, understand that your content will also almost surely need to be fashioned into stronger content: content that draws in audiences, draws in Google, encourages people to share, induces people to hop onto your list and follow your socials, and content that (in sum) turns traffic into valuable assets for you (subscribers, followers, people hopping onto your offers). Last: learn everything you can about blogging, traffic, and converting traffic. Use the resources here and beyond WF.

Cheers,

Tom

use free & paid buyer traffic

Unfortunately no one will be able to answer.

IMO here's what you should consider focusing on:
Content
Link building
Networking within that niche
Social media presence

Post long content on your blog site - 1000+ words each blog twice/thrice a week.

What would you do in "4 hours daily"?

How much time should i give to my blog daily? This question won't have the specific answer. Because it depends on your ability, your patience and your creation. You can work only 2 hours a day with your website, your site can rank. But you have to remember that SEO is a long-term work, your private new site may rank after 3 or 6 six months. You need to make your content more fresher regularly, redesign your site to make it friendly to visitor and google, work hard on SEO and always learn to update the newest knowledge about SEO.

For me, the key factor to increase site traffic is to produce quality content. Your content is one of the essential parts of your website. Good content has the ability to drive people to your webpage. It is probably the best organic clickbait that encourages people to visit and check out your site.

Loren

Consistency and actual good, in demand content that is sincerely valuable to your readers. You need to understand your audience like you understand yourself. Know what they want. Specifically. Know what they are craving to learn about and deliver. Search engine algorithms are very smart these days. You will get rewarded in the SERPs. That alone will give you a heck of a lot more traffic. Your posts will get shared also.