Hi @Jason_Fujinaka ,
Yes the current limit of options within a single-sleect or multi-select field is 500. Refer to this post for all limitations.
There, you will also find the limitation on Portfolios is 100 for the Advanced tier (currently unlimited for legacy Business tier, until it is phased out) but unlimited for Enterprise tiers. So portfolios may not be a scalable solution for you. Instead, you could use Teams (which are unlimited for all tiers) as containers for Customers, and instead have a CRM type project where each task is a customer.
Regarding the VLOOKUP that you mention, you may want to add your vote to my post here. This would be a really cool feature, but until then, you may perhaps be able to leverage Zapier’s Tables feature or lookup tool for something like that.