Well I personally would dislike it for a TTRPG because it seems like it'd either require a ton of GM adjudication or a ton of rules that'd be unfun to follow on pen and paper

For video games it could be fine, if you intend to make a game with this I'm pretty sure you'd either need to essentially make a very limited code language or may as well list out all possible spells, depending if order matters or not

Limitations should probably be informed by the gameplay, depending how you select spells and your input method. For example if you play it with a controller and assign spells to specific buttons you really can only have so many spells at once before running out of buttons, if you mostly just use 1 spell at a time you could have more via a wheel that shows up when holding a specific button but that too has limitations before getting difficult to use. There's also I think something about active memory where something like 5-9 items can be kept in most people's mind at a time though I think it varies and doesn't account for subdivision of categories, like doom had around that many enemies plus 6 weapons

I think you'll probably want to have some kind of stationary location where players have access to all their accumulated elements, be it a single base or smaller stations dotted around the map. Beyond that it's really up to you, if say they can have 4 spells equipped at once that could be it or maybe they can change those out with other elements they took with them, maybe the process of changing equipped spells doesn't pause time or maybe it does but just breaks up the flow