I've been pondering Citadels a lot lately in regards to how to fit them into my small time industrial operation, or even if I should. Here's my train of thought.
A lot of people are going to purchase Medium Citadel BPOs on day one and start building them. That will drive prices for the components required to build them, while the excessive competition to build them will saturate the market and drive prices down, quickly eating up profit margins. And then assuming I can get about 15% profit on each unit (~100 million ISK let's say), I'm looking at having to sell about 60 of them to start to get a return on the investment into the BPO. And that's assuming I can get good prices on the structure components I need, or look into getting the eight Structure component BPOs I need, either unresearched at ~200 mil each or researched at around 350-400 mil each (if I'm lucky). In other words, it feels like a large investment for possibly small returns.
The other alternative is to simply buy the Medium Citadel BPO and put it into research for the next year to make copies of later on once its at ME10. I'd still be tying up ~6 billion ISK for a year but the returns on the copies are certain and I can resell at a profit if desired. Plus it gives me time to allow the market to settle and evaluate at that time if building Citadels is profitable enough.
But wait! There's more!
I've been alternating building Archons and Moros, but the new Force Auxiliaries are coming and with them will be new BPOs to consider buying. I figure I'll need to get at least the Amarr version, the Apostle, and I'll probably consider buying two so that I can stuff one into the year+ researching time to get it up to snuff.
Here's the Archon BPO that just finished researching from ME9 to ME10. Check the install date versus the end date; almost 10 months, and that does not include the time to get from ME0 to ME9.
TL;DR: I'm definitely adding a couple FAX BPOs to my library, still on the fence about the Medium Citadel BPO plan.