How often do you do water changes? The nice thing about 45 gallons is that you can easily rely on water changes for most of the "keeping it clean" aspect. The fuge is nice for lots of extras, but you can easily manage a 50% water change with a brute trash can, so if things get out of control, you can replace water rather quickly.
The smaller water volume will mean larger swings with the evap, so I agree with the above. Get a good auto top off.
Right along with that, make sure you are topping off with 0 TDS in the water. Again, smaller water volumes, so every little thing will count more.
Lights are really a personal decision. You can grow all corals under all of the available lighting options. Just be cautious as mentioned before that LEDs can easily burn new coral and everything will need acclimated.
I ran my 40g breeder for 2 years with a HOB skimmer and power filter. Used a 6 bulb ATI T5,a bubble magus doser (ESV 2 Part), and a Tunze ATO. Tank was packed with all sorts of coral. Kind of miss the simplicity.
Also recommend a good variable powerhead. MP10 or Jebao RW8 would be nice I think. Just make sure it changes throughout the day so you dont get heavy spots where nothing grows. Does your power filter have a surface skimming function? That was a must for my HOB skimmer. Hated the film on the water surface.
Keep it simple.