Hi there, I finished playing through Sacred Trilogy the other day and loved it! Sacred Stones was my first FE game so has always held a special place in my heart.
If you ever manage to implement 3 promotion options that'd be huge, access to some of the enemy only classes like Gladiator, War Monk & Dread Fighter would be super fun, as well as diversifying everyone's class (and therefore skill) options nad making more classes widely available (and just as a small hope, giving Pirates or Fighters access to Summoner would be my number great, the class has such a cool axe animation but the two possible summoners have no real reason to ever use it without severe use of stat boosting items)
With that aside, I have some feedback to give on my experience. For clairty, I'll note that I played Normal difficulty, Random Growths, and Ephraim mode:
-With the addition of the skill system, most classes seemed well balanced so you don't have the situation of the base game where there's usually a superior class choice, my General (Gilliam) was actual a very important member of the team thanks to provoke and the high defesnes (at least until I got Duessel who did the same job better thanks to his high res) and the extra point of movement really helps. Though, while Wary Fighter is in theory good, my Gilliam actually ended up pretty fast (as did my Amelia, though she wasn't a general) so wasn't as helpful is it could have been.
-Staves on Rogues and Falcoknights was a very welcome addition, especially with how easy it is to buy physic staves, made the later parts of the game much less frustrating.
-The difficulty curve mas modest but not too wild (Though I did a lot of arena abuse so it probably would've been a lot harder without)
-I was skeptical about using the Lords' alternate promotions, but tried them out and loved them. Ephraim having full weapon triangle control is great, and Eirika's magic damage output is surprisingly high (though could have been better, but hey, that's true of Eirika in general.) In any future runs Its highly likely I'll use their original promotions, both for the extra movement and my aforementioned love of staves (Though this is assuming they get the same class skills as the new promos, curious if they get anything different), but these are still good.
-I often found my Convoy getting full which was really frustrating, and I had a tendency to not use stat boosters until a unit is max level so I don't 'waste' them (Though with how easy they are to get in postgame I know I should be using them as I play to save space and get stronger) so I wonder if it's possible to make the convoy larger.
-While I conceptually like Discipline+ as a skill for Kings, one of my biggest gripes about GBA FE was not being able to S Rank multiple weapon types so its a shame you still can't in general, was something I would've liked to see but I understand that's not the vision you had. At the very least, might have been a cool idea as a class skill for Unmounted Ephraim as tehcnically a King (perhaps give Eirika's mage lord something similarly good to further set apart the mounted and non-mounted classes)
I also have a number of thoughts having played through Lagdou, but will keep them in a spoiler tag for the sake of keeping the surprise alive for people that haven't played that yet:
With all said and done, I hope my feedback is helpful and, regardless of any comments and criticism I had I want to make clear that I absolutely loved playing the hack and appreciate all the effort you put into it!