So I’ve got a client that has like 100 custom fields in the Opportunities module. I’m already concerned with performance. In list view, exports, imports, deletes, it’s really slow. The client wants to add another 100 fields to Opportunities. I’m thinking this would be better done in another module. Anyone have any experience with such a large number for fields? Is my instinct correct? Or am I worried about a non issue?
IMHO, 100 custom fields is always a database design error. Don’t get me started about 200! 
It usually means that they are bringing data over from some legacy process like a 7 page paper form or something, and are failing to see the data for what it is.
Either it is meaningless, store-and-retrieve stuff, and you could put it all in a single large text field, or it does have meaning and they need to go looking for ways to group it, detect entities, repetitions, etc, and separate that into different records of a related module.
Thanks @pgr so I’m on the right track. Yeah they came over from Salesforce and use Opportunities more like a contract module. They sign up large apartment buildings on contracts to manage their utilities. There’s all kinds of info they need, I’m trying to split it up into “buildings” , “opportunities”, “Contracts” and “Account Info” for all the accounting stuff. It’s a struggle!