OK, have some feedback on the castes now that I've played a bit.
First of all, overall I really enjoy it. I like the slower 'default' skill gain, and I liked that dwarves arrive with much lower skills. A frustration I've always had in vanilla is that you spend all this time developing a dwarf in skill X, and an immigrant walks in one season later and he's a freaking master. Or, some other dwarf gets a mood and goes from Dabbling X to Legendary X, leaving the guy you worked on in the dust. All that work for nothing. I feel a little prouder of my dwarf development now, and I like the control I have over the process via the guilds.
I have two suggestions regarding tuning:
#1, the requirement of gold coins makes some embarks behave drastically different. You either are swimming in gold if you have an embark with natural gold; or you are reduced to scraping it off of each dwarf caravan. On a gold-less embark, I had to go the caravan route, and it was very slow going. The problem is, I simply could not get a caravan to bring enough. I could 'guild' maybe 5-10 guys a year, and never mind the military for many, many years - the 5 bars necessary was too steep. Yet on the next embark, I had gold veins - and suddenly I could guild anyone I pleased, no problem. The play difference is night and day.
Possible suggestion - any way to add gold bars to the other caravans? If not, perhaps a crate of gold option? Are other coins like silver possible? Gold-less embarks need a little help.
#2, military and the castes. I play very military-intensive embarks, with tons of invaders, so I tend to go whole hog on my military - I have close to 100 towards the end of a mature fortress. I found the 50% learning penalty pretty challenging, particularly with early invaders. Learning rate for military has always been a notorious complaint for DF and I worry that people may find it even more exasperating when coming to MWDF. The 2500 gold to remove only some of the penalties feels a little steep, although the benefits are certainly nice. That's just a lot of coins though when I've got up to 100 guys.
Suggestion - personally, I enjoy the early challenge of the 50% penalty, so I would dearly love a cheap Military Garrison option of say 500 coins to 'Undergo Basic training', which simply removes the -50% penalty across the board. This would allow us to fill most of the military ranks with 'basic' soldiers who are the same as vanilla DF soldiers; interspersed with super-soldiers like the Legionnaires, Guards, etc.
BTW, love the metal changes you made, they play great. Thanks!