How to transition new laminate flooring to old flooring under kitchen cabinets?

Hi everyone,

I’m currently installing new laminate flooring, but I’ve hit a bit of a snag.

As you can see in the photo, there is some old laminate flooring left under the kitchen cabinets/appliances. I can't reach deep under the units to remove all of it, so the old boards will stay there.

My plan is to cut the old boards in a straight line and start the new flooring from there. A kickplate (plinth/baza) will eventually cover the dusty area, but I'm worried about the transition between the old and new boards.

A few questions:

What is the best way to cut the old boards in place? I'm considering buying a multitool (oscillating saw) for a clean plunge cut. Is that the right move?

Should I leave an expansion gap between the old and new laminate?

If there is a slight height difference (leveling issue), what kind of transition strip or T-molding should I use so it looks clean once the kickplate is installed?

Any tips or tricks for a seamless look would be greatly appreciated! Thanks in advance.