Just to be clear: there are better ways of doing this but as far as I know they are not widely used (yet!)

- You can paginate the follow list request using since/until with timestamps

- Relays can support COUNT https://github.com/nostr-protocol/nips/blob/master/45.md

- Clients can outsource pagination/aggregation to DVMs https://www.data-vending-machines.org/kinds/5400/ nostr:note1swd6s64mjk8mfys9m7n78s5j6q0szqp984sdlcmtfv799tnr4ltsj3tglu