Down the rabbit hole! I don't normally recommend Wikipedia as a source, but their page on ceramic capacitors is pretty good once you've scrolled down to the Applications and classes topic. For ceramics, the dielectric makes a lot of difference in behavior. NP0 (CG or C0G) ceramics are the least likely to be microphonc, but are avaialbe only in very small cap values (and mostly surface mount). X7R are less tolerant of microphony, but are temperature tolerant and available in values commonly used in valve amps. And their are many others, all with advantages and disadvantages. I've quit using Mallory 150's -- they're the old standard, but I think the new radial film caps are more stable. I particularly like the Panasonic polypropylene caps which are small and sound great. Of course everyone likes the Orange drop 715 series -- they sound great but are garish and fat. Andrea's BOM is already there for you. It's a great starting point.

With regard to ceramic caps, I'd focus on the dielectric used rather than the brand. C0G and X7R dielectrics provide more stable response with changing temperature than some of the others, but you will have to do some of your own research. The good news is that there are exponentially more choices for radial caps vs axial. It would be nice if Andrea would provide lead spacing info, but in fairness he does provide a comprehensive BOM with each board -- which you should use as a reference.

The Hammond 194B will work just fine (I use these all the time). The reason it will work is that the current that passes through it (the 90mA part of the spec) does NOT supply the power tubes. The preamp tubes draw very small amounts of current. If you're in the US, try Hawkusa.com. -- best prices, great shipping.

One bit of advice that really helped me was to print the layout in Tabloid mode (11x17") -- not having a large format printer, I sent this to Fedex, cost was low, and the increased size helped immensely.