I do not think I could give an accurate conversion between FPGA Slices and transistors myself, it is certainly small (23 slices) and processors with similar cap

I do not think I could give an accurate conversion between FPGA Slices and transistors myself, it is certainly small (23 slices) and processors with similar capabilities ran in thousands of transistors/tubes range. You should look into more esoteric processors such as Forth CPUs, other bit-serial CPUs, CPUs built around single instructions (such as SUBLEQ) and new CPUs built out of 7400 series parts.