Light, T5ho would be fine.

Skimmer I would go with a rating of 2x water volume. Make sure it will fit the sump.

Sure you can use base rock and seed with rubble or a little live rock.

Substrate you really don't need more than 2", I prefer pretty fine (not sugar sand) and stay away from crushed coral, pain to keep clean.

Sump how you set up baffles will depend on your skimmer and the other things you want to do. Pretty small sump for a DSB. Million ways to go for sump layout.

Livestock, I'll mostly leave that alone, but a fox face will get too big for a 60g. And if you do an eel you better have a very well sealed lid, or it WILL go carpet surfing.

In tank flow will depend on what you end up with for coral. Flow through the sump need not be high, don't rely on your return pump for in tank flow.

Take your time and enjoy the process, don't rush to make the tank look complete all at once. And avoid impulse purchases.