First draft, I will add to this once I'm further but since I know you have a tight schedule, I thought it better to start typing early.
NB these are of course just my opinions and may not at all match other peoples':
1: You can use items to boost stats for upgrades. I like it, but can be exploited by keeping all stat boosting items and swap around before learning skills. Ie adding an axe wiht +5 strength to a weak druid to learn Shield skill. I wouldn't change it, but as said, might possibly be exploited in late-game when you have enough items to get all skills for all characters (that fits class of course). Haven't tested if it works with the "prestige classes" though.
2: I know there's a button for skipping turn as I accidently did once, but I can't for the love of me find it again. Maybe have it more visible with the other actions in the panel to the right? Sometimes I don't want to kill an enemy to make sure I heal up fully before ending the fight to save on Rest.
---> Alternative: Allow Skip/Pause? Let the player choose "pause" to put their character at the very end of the Round (for example to buff up them even if they have higher speed then the buffers)
3: Pacing is perfect. Wouldn't change a thing. Leveling has just the right pacing for me.
4: Perhaps some spells are a bit to pricey. I have three spellcasters and they all at level 21 still use their level 1 spells. It's rare I can afford 2000 gold for a spell after also pumping 1000s of gold on Mastering skills. This means you need to grind fights to get gold, and that gives you more exp. If I do (I haven't much yet) I fear I might be overleveled later? But perhaps you have an exp diminishing return that I haven't noticed yet for lower level monsters.
5: I play Druid, Monk, Sorc and Assassin.
--> Druid: Very weak so far (level 20). BUT their special ability Fumigation carries my Sorc and sometimes Assassin. Other than that they just heal a bit and maximize damage on friend. One trick pony since it's not possible to afford spells for all characters and I have prioritzed the Sorc. Unsure about Shaman prestige class special skill. Didn't seem better then fumigation, so opted for stats.
--> Monk: Similar to Druid in a way. Great special skill Prayer, and then just used for healing and the ability that maximize the damage of a party member. Priest upgrade special ability sucks. Sorry to say it, but Prayer is MUCH better than the "free healing" that should be better. SHould have taken the stat points instead for sure. I am recommending you to replace Free healing with something else, perhaps a party wide buff of some sort, ie +5 to Endurance for all members or similar. Prayer will always be better otherwise.
--> Sorc. Still the best class I've tried so far. Fire arrow level 1 spells is what carries the game just as the earlier versions I've tried. Just now at level 18 I bought fireball, but still I use fire arrow a lot or even more. With fumigation adding Int damage, Concentration allowing spells to be cast every round, Sorc is the "DPS" of the team for sure. Upgrade to archwizard I opted out of the new skill since I always use Concentration to save on mana potions, so never tried it.
--> Assassin: Ambivalent.. the skill is graet when it works, but I feel the 30% is quite low. SOMETHING should allow us to up the % a bit, Dexterity/Speed/Strenght or something.. it's just to much of a waste to loose a whole round doing nothing when it fails. The Shadow skill is pretty decent replacer, but better for a team with more Melee than I have since the +8 damage adds to everyone else's attacks too. Great choice, keep it.
Gotta go, will come back later and edit.
Edit: Random notes for now while playing.
* Druid/monk spell Partner Blessing doesn't trigger for Fireball which is quite annoying. It looks like it triggers for Fire Arrow spell though. Intended?
* Assassin Attack with Panache has lower damage than the regular attack, or rather it seems fixed but less than in the middle between Min and Max (ie 35 when I have a base attack of 25-45 minus enemy End). My assassin has 35-64 damage and Panache has 46 fixed damage. This makes me not use it since higher damage -> faster battles --> more battles in the same time period -> longterm better than trying to squeeze out a few extra exp/gold points per battle. Classic ARPG style of play perhaps, but speed is progress after all.
---> The more I use fireball I feel it's bugged.. instead of hitting for between 50-100% of your INT, it feels like it always hits at 50% ? Or I am the most unlucky dice roller in the world.
-------------> Edit 2: Ah, I see you don't let elemental mastery affect fireball, so that's probably why it's so low damage. I think you should change that as it becomes obsolete at the same time as you can afford it. I always go up against ~3 enemies with 200 HP now and doing 18-32 and hitting for 25 damage x 3 is pitiful and a waste of a round.
Since I'm mostly testing I spend the coin on Levitation and lockpick expert and went back to the old islands to try and remember old chests and clouds to scale. Found one at least and that was quite fun. I know I've seen at least one more cloud to scale but can't for the love of me remember where
---> Crazy idea? Add possibility to add notes to the map for reference? Or in the journal/quest. Sometimes a master lockpick chest is deep in a jungle and I just can't remember which area to enter after I have the necessary skill.
My guys are level 25 or so now and just finished the Frost Island quest (mausoleum). So far I've found most bosses very easy, 4 vs 1. The only tough one was the first green dragon which was level 20 when my team was level 12, had to come back later to finish him, but all other bosses I've taken at first try (IIRC).
Seems like my team is pretty well-rounded but as I level more and more, Druid and his Fumigation skill get's less and less needed and now he's delegated to just healing and slinging the occasional fire arrow. Monk, Sorc and Assassin all scale very well. Quitting for now, will come back again later.
EDIT 3: Fighting the last boss now and I found such a sweeeeet light exploit I wish I knew much earlier: assassin special skill Blood for Bleed + Fumigation (druid) + Blessing (monk) let's me attach twice for ridiculous damage (almost 300 damage to Furax himself in the second round) and then in the next round my Monk or Druid cast Cleanse negative effects and remove the Bleed (-101 damage) on assassin! hah, wonderful! So I could kill Furax in round 3.
Here's my end chars etc