Assuming you're thinking about earning Lightning transaction fees: I don't think there will be much of a profit in running a Lightning node, so the amount you want to keep locked in a channel will mostly depend on your actual spending habits. It's still a bit early to tell though.

In this case I'd give Lightning a run on testnet first

A few starting points:

1) HTLC.me web wallet
2) Eclair testnet android wallet
3) Lightning Desktop App ( https://github.com/lightninglabs/lightning-app/releases )
4) yalls.org for spending testnet microtransactions
5) Starblocks.acinq.co for spending testnet microtransactions

1) and 2) are easiest to get into, but rather limited in functionality.
3) Seems to be fully fledged, but I had connectivity problems when trying to open a direct channel. Might have been a firewall issue though, since it was not my home network when I first gave it a try.
4) yalls works great so far
5) starblocks had connectivity issues last I tried

I'm sure there's more, but that's how I personally got started.