OK, I got the tiles (25mm x 40mm) with 5mm gap up on the kitchen wall
above the work surface.

Next stage is to do the grouting.

Do I need special tool for that or can I just make up grout mix and poke
it into gaps with my finger and smooth off with, say, a pencil? With
such large tiles , it doesn't seem to be need for a grout float?

Do I fill the horizontals first or the verticals? Or does it not make no
difference?

I am minded to fill internal corner joints with silicone instead of
grout. Is that the recommended way?

Also, fill the joint between work surface and bottom row of tiles with
silicone bead? Is that good/bad?

Ed