Wordpress Layout, images, columns, mobile view (site cleanup)

I need someone to check my WordPress website and make sure everything looks clean and even on desktop and mobile.
It’s mostly about fixing layout, columns, and image sizes so the pages look the same across the whole site.

My WordPress site is primarily based around "clicking on images" to take you where you need to go, currently some of the images inside some of the columns are different sizes (see attached images) and aren't stacking properly that it looks untidy, so I'm looking to make sure that it's aesthetically pleasing, and the images are large enough on a mobile device but the layout is very similar to the desktop version. I have found that rows that have three images in the columns are the best size and look the best on a mobile device but as you can see, the gaps vary between columns and images (see images).

My perfect size and layout is the pink images, top 2 rows, the size and gaps are what I would like have across the board on all pages.

On pages where there are lots of images, I would like them all in rows of 3, same layout as the pink top 2, just with the gaps smaller between the title of page and footer please.

Please make sure:

All images are the same size, not stretched, no big empty gaps between columns (as described above)

Columns line up properly,

The site looks good on mobile and desktop

When you click between pages, it goes back and forward (no new tabs opening)

I’m also purchasing appresser app, so I want to make sure everything flows well and looks good there too. The mobile experience needs to feel smooth and consistent.

This is a basic layout and mobile optimization job — no big redesign.

I want to agree a fixed price before you start.
Please tell me your fixed price and how long it will take.