No one likes left over. The capable one will definitely not take a bite since there is almost nothing left.

In China it is almost std practise to use spacers for tiling.
However in here its hard to get a tiler that uses them.

https://www.facebook.com/videohddailly/vide...29678988240604/
She uses spacers, back buttering.

If its a small area u can DIY geh. levelling by laser easier, or spirit level and plumb line/45deg set square coz herringbone is all diagonals. Material wise sika tile cement + PVA adhesive (latex adhesive/"susu") je. Best to sand down all the paint so it can bond to cement of the wall, as paint won't really hold well. https://s.lazada.com.my/s.Xp6yY
PVA adhesive sikalatex comes in 4L tubs.
Cutting the tiles will need a marble/tile cutter. Manual one also about 100 bucks, power tool 80-100 or closer to 200 for stanley, makita.

Yes the sika premixed tile adhesive (that 25kg bag) just add water will work pretty well.
The sika premix tile adhesive is a ready mix of cement and other modifiers inside, its easier to just add water to it - as compared to making your own mix with normal cement ($16 bag), add sand add this add that more things to go haywire.

P.S. Don't add PVA to the premixed stuff (apologies); i confused PVA with latex adhesive. I read PVA may mess with the pH coz it produces acetic acid which is the other way (cement needs alkaline env to bond and harden). Its own Sikalatex (as mentioned on the 25kg bag) should be safe.
P.P.S. PVA glue and latex glue looks the same but are 2 diff things.