"Bitcoin and Bitcoin Cash have become two prominent players in the world of cryptocurrencies"

no they don't... Bitcoin is only one, Bitcoin Cash is scam... it's that simple

IMHO you should consider to add relays of well known clients (most of them are running own relay) as...

wss://relay.damus.io wss://relay.snort.social wss://relay.plebstr.com wss://nostr.rocks

also aggregators like these make some sense to me...

wss://purplepag.es/ wss://relayable.org

then you can consider adding some paid relays that bring a special feature or will be more persistent...

wss://filter.nostr.wine wss://eden.nostr.land wss://relay.nostriches.org

go for Trezor https://trezor.io/ ... it's father of all hw wallets, all open-source including hw

that's a bit contradictory, but you can try https://phoenix.acinq.co/