There is no limit, and no cost. Creating an alias is the intended default, not an advanced feature.
A practical way to divide them: one per context rather than one per service. Work, private life, a hobby community, anything you would not want linked together. Someone who wants their professional and personal lives kept apart needs two aliases, not two identities.
Why more is usually better than fewer. Each alias is a boundary. The more you reuse a single alias across unrelated services, the more those services could theoretically have in common to compare.
Deleting an alias removes its data too. An alias can be purged from the network entirely, including every data node stored under it. If an application stored your settings or profile on that alias, that information goes with it.
So before you delete one, ask: is there a service I still use through this alias? Deleting it is not the same as logging out — there is no version of it left behind to return to.
Your Core ID is unaffected. Deleting an alias never touches your underlying identity.
Manage them at uiid.me.