Well, I'll wade in with my 2 cents.
It's my opinion that there's a progression to these things. Whether making points or improving the realism of our trains, I firmly believe you need to walk before you can run.
I learnt the trade on 00, making a decent layout a few years ago using Peco code 75. I then moved on to making points in copperclad - successfully (even a double slip
) which boosted my confidence no end. I have made several etched loco chassis so I am comfortable with that...now.
My next foray will be EM (whenever I get round to doing that
However EM and P4 are quite different systems despite being less than a mm apart. With EM, tolerances are finer than 00 but not dead scale. It is my belief that current RTR loco wheels will work on EM (the purists may disagree) - this reduces the cost (a steam loco wheelset from Ultrascale will run you around 70 pounds) and effort of conversion hugely. You HAVE to replace wheels with P4 - and usually rebuild the chassis (unless you can use the Easi Chas from Brassmasters)
At some point, I don't rule out doing something in P4. A mate of mine who has a very nice P4 layout, told me he regretted going P4 because it is a lot of bother.
So, Sean, you'll need to assess your goals and current skill set and get to grips with this. My only concern is if you try for that "bridge too far" you'll be disappointed.
Oh, as for the brass chairs, Cameron, those in your link appear to be lost wax brass. I have seen a system demonstrated in MRJ that has the builder folding up each and every chair from an etched fret (can't recall the supplier) - seems rather a lot of work to me, despite looking brilliant.