I would strongly suggest waiting on a reef tank. I did them for years and they cost a lot of money to set up and run and you can't skimp on lighting (which is very expensive for a tank that size (I have one) and all the equipment. Plus factor in salt and possibly needing RO water, a lot of different test kits, and the livestock is not cheap either. You would do best to concentrate on this planted tank for awhile and not overwhelm yourself trying to run two different types of large tanks.
Honestly I'd do a WC to bring down the nitrates again then redose ammonia.
The tests are easy. Fill water to the line, add 1 drop and shake and continue to add 1 drop at a time and shake until the solution changes color. It tells you on the instructions what is the starting color to what it changes to. Be sure to COUNT YOUR DROPS as this gives you the KH or GH reading. So if you added 4 drops and the color changed then your KH or GH would be 4.
And yes, add the root tabs once you plant your swords, crypts, or bulb plants.
I'm not questioning I'm just curious. Why do a WC now? Does it help the cycle?
It's better to keep the nitrates somewhat down so you don't have to do several WC's down the road to try to lower extremely high nitrates.