Tank size is really up to you. Bigger is better due to more water, which keeps things more stable. I would go with a sump for anything over 30g, but you could use one on a smaller tank (again, adds to total amount of water, which is good). The other fish you want will play into the size decision too. What are you considering beyond clowns?
For lights, I'm a fan of the LEDs sold on eBay (TAO knockoffs) for about $125. Each will cover about 2' and work fine for corals.
Put money into the budget for an RODI
water unit, as it will save lots of money over buying from an LFS
Beyond the "going bigger" for more water, you will also want to consider the addictive nature of this hobby. Your smaller tank will very likely become larger as you fill it up with fish and/or corals. My 75g lasted about a year before it needed to be a 240g (with an additional 60g cube in the bedroom).
. Buying larger puts the upgrade further down the road.
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