Did i cycle my tank properly? Getting ready to put fish in

Hi all, first time fish keeper and to make it hard on myself, I got 8 dime size discus heading my way. I have a 150 gallon tank with a sump, very light substrate and only 2 java ferns. There are no other fish in the tank at this time.

My question is about how to tell if I cycled my tank properly. Instead of something off the shelf, about 3 weeks ago i dumped in some water from the washed out media of my friends established tank. I added 3 cap fulls of prime and i feel the stupid move I made was adding enough Acid Buffer to bring my pH from 7.5 to 6.5. I've since realized I should probably not have added the buffer. Also, I have topped off maybe 5 gallons total with straight tap water.

My current parameters (in spite of my colorblindness) -
pH - 6.8 (i think because I topped off with tap water)
NH3- 0 (or .25ppm, hard to see)
NO2 - 0
N03 - 0
KH - 2 drops with API kit (not sure how to convert this to ppm)
GH - 12 drops with API kit (i think 214ppm)

I have a RO unit from Jack Wattley on the way and I'll be using RO water mixed with tap for water changes.

Any advice on what to do prior to putting these 8 in on Friday?

Thank you in advance!

Well dime sized discus are tiny. I would start them in a smaller tank. I’ve got 8 2 1/2” in a 45now and that’s what I’d recommend. These are your first fresh water fish? What type of filtration are you using? What do you plan to feed? I use freeze dried black worms. Plan to feed a lot. Again I’d start them in the 45 and change 50% water daily. With them coming on Friday you will be doing a fish in cycle. They will get lost in a 150. You need to grow them to at least 3-4” before putting them in the 150.

You could put a divider into the tank. I would even use a divider in a 45g. You keep the fry closer together and the food will not be spread all over the tank. Then you can expand the divider as they grow.

I'm afraid to say you are a little ahead of yourself here. You have 0 nitrates which means you have no biofilter. The bacteria you added from your friends filter media 3 weeks ago are long dead because they had no food (ammonia/nitrite). Bacteria need a food source to survive & multiply. In a fishless cycle you need to add ammonia to feed the bacteria to establish a healthy sized colony to support you fish.
I would advise you read up on the nitrogen cycle so you understand it. It's not complicated once you get how it works. You do not need to use RO water, it is not necessary. All you need is a stable pH and you discus will be fine.
It is far from ideal to try to grow young discus whilst your filter is uncycled, but to mitigate possible ammonia/nitrite poisoning you would need to undertake a minimum of 100% daily water change while your filter gets established. For this reason, starting in your 150gal is prob not ideal due to the amount of water you will use. I recommend a getting a 40 breeder with the filter you plan to use in the 150 and starting there.
You're going to need guidance as you progress so please keep us up to date as to what you're doing and how it's going. We want to help you succeed, but you have definitely chosen a tough road for your entry into fish keeping.

I hate to be the bearer of bad news and I hope that I am wrong but it is unlikely that they will survive. Noting to do with cycling or not. I think it is a big mistake to sell someone dime sized fry, unless the recipient is very, very experienced. There's someone on aquabid who offers dime sized fry and claims that its better to purchase at this size because of decreased mortality in shipping at this age and size. BS if you ask me.