Unless you know that the overall solution you are going to go for works well on a tablet you should assume you're going to need a laptop.

Firstly the laptop is going to act as an immediate repository for your photos and videos, then you are probably going to adjust the photos and videos in some way, for example cropping the photos, reducing the overall size, playing with the resolution and compressing videos.

It's better to compress videos on the laptop before you upload them to wherever they are going to be, otherwise you will be sitting around for hours on a slow connection.

And as others have pointed out you need to create and edit your text. Yes, it's possible to do that on an iPhone but even with the larger size of the iPhone 6S Plus it's not much fun.

Where do you learn to blog? Well there's two aspects to this, one is the ability to tell a story in an interesting way—use simple sentence constructs, write as if you are talking (Google 'how to write a blog'); the other is the technicalities of which blog software to use and how to actually post.

I'd suggest you look at Wordpress as a start and to give you an example of a Wordpress blog written by an absolute non-technical neophyte, here's one from my daughter about her beloved Cockapoo! with 29,968 visitors to date.

What's important on a blog isn't the design or layout, it's the information it imparts.

__________________
"For sheer delight there is nothing like altitude; it gives one the thrill of adventure
and enlarges the world in which you live," Irving Mather (1892-1966)