Laying Ceramic Floor Tiles on Floorboards?

im a builder in uk ..have done this type of job dozens of times ..first ..all floorboards must be sound and well fixed ..ply needed 6mm ..does not need to be thicker ..but must be well fixed .staples or screws ..every 6-8" ..all over ..that's a lot of fixing ..but it must be solid .you must use flexible adhesive and grout ..ordinary will crack out ....modern cutters are not expensive ..20-30 pounds will get you a small electric cutter with a diamond wheel ..you will not snap floor tiles with the pencil method ..and nibblers struggle with the thicker tile ..go to your local tile shop ..they all ways have tools to hire