Ike's approach works for Ike's selections of coffee and expectations from that coffee. If you have different coffees or expectations, you may need something a bit more controlled. 20-30 seconds might be appropriate for a "dragon", but shorter flushes are generally more appropriate. I typically would...

La Marzocco Micra - Top-quality shots - Very forgiving - Ready to use in under 10 minutes

I've only used the Moonshine 64 mm Mizen, not the media-blasted ones. I'd put the ones I have in roughly the same category as the 64 MPs in this context

Budget? Preferences in espresso? How long are you willing to wait from deciding you want an espresso to being able to pull one? Otherwise you'll find a three-group La Marzocco as one of the best choices

It's a "try it and see" thing. I've found the dose for a given basket to vary a couple grams across different roasts, without going any darker than a medium or so

Kingrinder at $100 or so is another option. Looks like Amazon US has the K6 at $100 after a coupon right now

There are some great cross-sectional illustrations at "E61 Group Espresso Machine: Detailed Interior Schematics" Drilling down into the cam chamber and then up from the dispersion block recess seems like a very reasonable way to get the two connected reliably. Still no drill bit that I know of that ...

Now all you need is a friend with a machine shop so you can tap into the group head for a thermal sensor and keep the manometer in the now-usual place. Somehow I don't think the E61 designers thought of that hole as anything other than a manufacturing necessity

The Atom 75 burrs, if "Mythos-like" in your market, are a step up from the 55 mm Eureka burrs. The Mythos burrs were considered to be top-notch burrs for traditional espresso. If you're staying with traditional espresso and traditional burrs, my opinion is that the big changes past the 55 mm Eureka ...

The Mara X measures near the outlet of the thermosiphon from the group head. It appears to be a reasonable proxy for the group-head temperature as the Mara X is typically repeatable within a degree or two in brew temperature. This is better than some E61-style DB machines. There is an ECM model that...