angle grinder to cut and clean tiles

Dremel

There are plenty of grinding wheels, too.

Don't grind the paint. You'll ruin the tiles.

Paint stripper will get the paint off the tiles, but you'll never get the paint out of the grout. Buy the Dremel attachment for removing grout, then put in new grout.

As it's on a curve, i need to cut a new

That will do the job fine.

Whatever you can find will do the job fine.

Nope, you'll damage the red surface doing it that way.

If the tiles are highly glazed, paint stripper should work, but you'll have to regrout the tiles because the grout will have soaked up the black paint.

Even a wire brush will damage the red surface, but is what you should use for that if you want to do it that way anyway.

Rod Speed, ye paunchy martyr slain in cupid's wars, thou lump of foul deformity, ye peeped: