HARVESTING plants has NO effect on stack size, yet still gives a little EXP. At first you disable "all harvest" to concentrate EXP on your farmers to pump stack size. Later, you allow "all harvest" to give kids something to do. Also... you do know that large stack sizes can't be brewed into barrels, right? I forget the cutoff, but I think its 6. You won't be seeing "Dwarven Wine [45]" at all. This is the main reason I just don't bother with potash. The other reason is that food is simply far too easy to come by as it is. I mostly just grow textiles and dyes. "Hunting" with my military squads and herbalist stripping trees and shrubs give me all the food/booze I typically use. Multi-hauling can allow herbalists to bring home 100+ units of plants a week or so... outpacing farms easily. Now if only toady would actually fix garden vegetables (can't even harvest anything with pods!), yet alone actually make hte different plants MATTER...
To the actual discussion at hand, I usually start to feel overwhelmed around 80 or so. Trying to find jobs for all of them is mostly just busywork... creating more miners to strip-mine more layers of stone to keep your 10 stone crafters busy. You then stud the stone crafts with bone and junk metal (*sigh* zinc without copper, lead, etc) to buy out entire caravans. The best part about this, though, is that more wealth=more migrants. It becomes a vicious cycle of busywork massively ramping wealth that attracts more migrants that need to be assigned more busywork... And that is how you get migrant waves of 60+ So not only do I keep wealth down to discourage mega migrant waves, but it keeps mega goblin waves at bay until your defenses are truly mature. I see 20-30-idlers and try really hard not to freak out and build 10+ more craft shops or extra textile lines.
Another reason I tend to have several idlers is that I rarely give dorfs more than one labour. I then try to get at least 2 dorfs legendary in every skill (to minimize a dorf being on break at hte wrong time). Even skills that don't have quality usually increase via speed. So out of those 30 idlers, you'll have a master mechanic, a legendary weaponsmith, a master potter, at least 2 animal trainers... all not so much "idling" but "on standby" for when I need them. I find if I give them 5+ labours each, then they might be all trying to make crafts when I want masterwork stone tables in hte dining room or a couple more mechanisms -stat- to get a bridge up.
Another thing to do is just throw everyone into a military squad... but I'll be honest. I -really- hate dealing with the uniform interface. This is especially true when I want bone (which is considered metal armor, wtf?) armors on my new recruits (that can't handle actual metal). However... I don't want dog bone helms and toad greaves with cat gauntlets and turkey and rhino leather tunic and boots. MY OCD WILL NOT LET YOU MIX ANIMALS! This guy gets the dog armor... this guy gets the toad armor... this guy gets cave croc... However, when I try to assign them specific pieces they never seem to bother picking them up. If I just leave it "metal" they raid the junk armor pile waiting to be melted down. This alone is why I typically build trap-master style fortresses that would rather drown, freeze, cast obsidian, run lead filled minecarts over, drop into pits, drop into pits filled with zombies/FBs/Titans, fling socks at, lead down repeating steel spike hallways... etc than deal with the damned military interface X.X
I would most definitely love smaller migrant waves. Maybe something like "the higher of 10% of your population or 3." You really shouldn't jump from 7 to 200 in a couple of years. I also prefer the idea of actively courting migrants. This could be tied to an agreement with the outpost liason as well- you could ask for no/minimal migration or to open up the flood gate. Perhaps the liason could even broker deals to get your fort to accept refuge groups if you are finally ready for a large wave. "The dastardly goblins lead by their demon master just overran a fort! These poor countrymen of yours need a new home! What can we offer you to take them in? Well... If you send me a skilled Doctor/Weaponsmith from the mountainhome I might be inclined to take them...." The migrant might also snub your fort and deter migrants for it not being prosperous enough (produced wealth, displayed wealth, too many nekid dorfs, no hospital, no tavern, etc). On that last note, there could be beautification/public works/comforts you could provide to attract migration. The more of these you build (statue gardens, zoos that track animal diversity, tavern, legendary dining haul, multiple temples, high quality bedrooms, etc) the more migration you attract as your fortress actually becomes a desirable place to emigrate to. Biome could also influence this, with rough biomes making it harder to drum up migration interest. How can you possibly get 60 dorfs to move to a horrifying frozen glacier 100 tiles away from the nearest town, but surrounded by goblin fortress and undead towers? It better have gold-plated latinum bedrooms with roc feather matresses and heated toilet seats... Anyways, the point is to make migration more dynamic and under player control. If you only want anemic growth, then you build minimal comforts and tell the liason to steer people away. Otherwise you pimp out your tavern/temples/dining rooms, build gold-brick roads all over the place, engrave -all- the surfaces, peasants get diamond encrusted beds, and everyone gets masterwork roasts and double servings of sun berry wine.
I'm starting to -really- get off topic now, so I'll hush XD