I once bought a set of vehicle weigh pads for work, weighed my then co. car (Audi A5), front/rear balance was almost spot on 50/50, but diagonally there was a (from memory) 25kg+ difference
Don’t get a chop saw, you’ll hate it! For what you’re doing an angle grinder will do, but for an alternative to a chop saw bandsaws are much nicer to use.
My Karcher is 14 years old and has been no trouble - it gets a full day twice a year cleaning the terrace and twice a month doing cars and bikes, no problems.
Good advice, I forgot to say I usually drill a pilot hole - it helps with accuracy too - going in with a 22mm drill can sometimes result in a hole some way from where it was intended…
I aim for 120mm - most stone round here is similar to what you have on the Cotswolds. For holes over 20mm I use a core drill but find it takes ages, so if using square bar I grind the corners off so I can make the holes smaller as others have suggested :D. I secure them with Fischer resin though...