Could I get away with just dosing with Excel (with CO2 and light) for healthy plants, or do I really need PPM Pro? I just ask because it will be another $40 if I get PPM Pro with a scale and RO water.
I think your problem is that you are expecting there to be a one size fits all method when it comes to planted tanks (which is understandable being new) but there really isn't. The hardware and plants you choose will dictate the angle of approach.
I personally don't think there would be any benefit from splitting up the photoperiod. Although people do it with some success I don't think it is overly beneficial for the plants as they have some chemical processes to carry out as soon as they are illuminated before they can take up co2 efficiently so shine light on them then off leads to instability initially at least.
Again whether you NEED PPS pro or any other water column dosing regimen depends on the strength of your light, how many plants you add, the type of plants you add etc. So for the most part planted tanks are about eyeballing your particular set up and making adjustments based on what you see. There is no guaranteed success and we are or have had issues ourselves.
I would say that try it. Find out what is in your root tabs. Which nutrients and supplement that ones that are missing.
Learn about your source water. Is it hard or soft? Does it contain lots of a certain nutrient to begin with?
I have just switched to soil which has many benefits but I still supplement magnesium, nitrogen, phosphate and potassium as my light is strong and the plants need lots of them. Also my tap water contains very low amounts of magnesium.
Try to learn about what the plants need and where they can get their nutrition from. Feeding at the root as well as the water column gives you a greater margin for error. If you skip the PPS pro and your plants are doing well what about 3 months down the line when your plant mass is 3-4 maybe more times bigger? Will the plants still survive on just root Fertilisers?
Get your co2 set up and running, don't scrimp on plants. See how they get on then make decisions based on your observations.
If the light is too powerful can you put something over it to dim it or lift it up a few inches to reduce the strength? Lots of things you can do.