@Baffa : I am in Ch.XII Elementals and although I like to participate - and perform as well as I can - in every Event (including Fellowship Adventures), which often necessitates using small Workshops and/or Manufactories, I very much dislike rearranging my City. For these reasons, and also because I personally find removing and replacing low-level Workshops and Manufactories tiresome, especially where City rearrangement is involved, I now permanently keep 10 x Workshops and 15 x T1 Manufactories in my City, all upgraded to their highest level before their footprint increases, both in order to maximise their output and because they look somewhat less out of place amongst higher-level buildings than they do at Level 1.
For me, playing as Elf, and taking into account best usage of small-building-appropriate space within the limits which my City layout currently affords, this means 10 x Workshops at L.4, 5 x Marble Manus at L.5, and 10 x Planks Manus (my own T1 Boost) at L.6.
This strategy has served me well over the past few Events and a couple of FAs so far, and of course has been very useful during the current Challenge, since the 10 x L.4 Workshops have been producing Toolboxes, thus taking much of the strain, as it were, without my needing to dedicate my 7 x Chapter-level Workshops to such long productions - which I would find unaffordable because I need a lot of Supplies to build Troops.
That said, and as you can see, this strategy is built around (a) the fact that I dislike rearranging my City (while of course there are others who love it, and many who don't really mind), and (b) my personal City build plus my overall gameplay style, which is both slow-progressing (I spend many months in each Chapter, so high-speed/volume Resource/Guest Race production isn't a concern) and highly Combat-focused - and so my strategy may not suit many others at all. However, in terms of being 'ready for anything' (within reason!), it works quite well - even though 'min-maxers' would certainly argue that devoting a fair bit of my City space, all the time, to low-productivity, low-level buildings isn't exactly efficient, to say the least...!
NB : A further reason why I've adopted this 'perma-low-level-buildings' strategy is that there is no doubt in my mind that Events of old and new types (including Fellowship Adventures) will become no less frequent in future, and may well - in my opinion, certainly will - become
more frequent, perhaps even to the point where more than one is going on all the time (as is the case in many large mobile games in Elvenar's genre).