I concur with what fishorama said re depth and hoe the swords are planted.
If one gets plants from a reputable source, the should come loaded with stored nutrients which will allow them do thrive initially. I would have waited a bit to fertilize. Swords make a lot of roots, so they take some time to establish when newly planted. They will not suck up a lot of ammonia until they do so. If you can grab some stem plants and/or floating plants, they go to work pretty fast. They also will take nutrients in via their leaves.
The old saying that "dilution is the solution to pollution" is your friend here. A 75 gal is way more than a bunch of small fry need. The volume of water alone will protect them. Then established (ammonia removal) plants will do even more. If you stick to the plan and do not rush stocking, you should have no issues at all. Just bear in mind when moving over a bit of stuff from the established tank that the bacteria are light sensitive. They prefer living in darker places. The means in the substrate below the surface, on decor that is shaded or dark. The only other thing they need is enough circulation to bring then what they need.
So when you choose a few things to over over, take things that offer the bacteria "shade." You do not need to move a ton of things over. The plants have already brought in some bacteria and a small amount of decor or substrate with bring a bit more. As long as you do not let the bio-load in the 75 get bigger than the bacteria can keep up with, everything will go fine.
You need only test for ammonia because if you do not see this you will not see nitrite and nitrate should not be a concern. Because you are doing some seeding of bacteria, you are adding both the ammonia and nitrite ones together. This means whatever amount of ammonia those bacteria can handle, there are ones which can handle the amount of nitrite that is created. Do not forget that any ammonia used by plants does not result in any nitrite or nitrate being created.
Perhaps the most difficult skill most new fish keepers need to master is patience. The lack of this is normally what causes a lot of issues in tanks.