Some basic patio questions

I'm looking at putting down an approximate 20m2 patio. It's replacing an older sandstone patio.

I'm not sure what I'll go with yet but want to avoid sandstone. My observation is that algae grows or something grows on the sandstone due to the grooves. It needs power washing regularly and looks poor during the winter when not done.

Looking at granite, porcelain or limestone. Would they reduce the issue?

For designs the have different sizes are they just larger tiles cut or are they sold like that? I haven't seen them.

I'd like to curve one side of it. Is it possible with all tiles? Is it going to add significant cost?

I'm not sure what the subbase of the current patio is but one or two are a little lose.

I've seen somewhere recommend putting down a concrete base. Is that just porcelain? More expensive I presume. Does it need to go down and cure for a while before tiling?