The LR will be your biological filter, housing the bacteria that turn ammonia into intrities and nitrites into nitrates. Partial water changes will have to be relied on to remove the nitrates and other buildup in the water column. That is fine for a FO or FOWLR aquarium. You could also run a mechanical filter (cannister or hob) if you wanted to.
Later you can add a sump and overlfow box to give you more water volume, a place to hide the heater and a place to to grow some macro algae. Next step would be to add a protein skimmer.
When you are ready for a reef tank you can add a quality light system.
It will important that you always keep REEF in the back of your head when you stock your tank. Don't buy anything on impulse (EVER)!. Always check to make sure it is reef compatible and always QT livestock before adding it to the main tank.
I basically took this path starting 5 years ago. I'm on my 2nd sump (replaced the original wet/dry with a sump) and my third light fixture.
I think you are ready to take the plunge. I can hear your new little fishies speakeing through the glass. "
Resistance is futile. Your life as it has been is over. Freedom is irrelevant. Self-determination is irrelevant. You must comply.
From this time forward, you will service us." 