I think the type of the diode is not very important here. It's in line to the 9v and it drop a bit the voltage and protect the circuit in case you connect it with soe PSU with an inverted polarity. A 1N4148 or 1N4001 can work fine, or 1N5817 is a very good option, too.
If you miss only it you can use a 47R or a 100R resistor or even jumper it, momentary.
You're right. I missed to write the Boost pot value. You can see it in the schematic, but it's a 10k log.
I need to look a bit better the schematic, but if I don't wrong with the boost at zero you have just the unity gain, so we can say if like that it doesn't boost so it works like a buffer. Usually, with the opamp, the inverting input stage has an input impedance lower than a non-inverting input stage, but if we see the R2 470k (and maybe R3, too) the impedance should be ok, anyway
Thanks for your work with this layout.
I build pedals