The loft progression of 3.5 in the long irons to 4 in the shorter irons is pretty common, at least for us. Stronger lofts in todays designs have made us have to rethink the progressions a bit, but 3.5 to 4 is normal. .5 degree would not be noticeable except maybe by the best of the best, but not sure they could either.
Gapping in wedges is totally personal preference. I play a 48, 52 and 56. I like the 4 degree gap and that is usually what gives you a normal distance progression. Also, you should evaluate what kind of shots you hit the most with each loft and adjust to what provides you with the distance and trajectory that you want. 6 degrees from the 48 to 54 could be a little too much, but night not, depending on the player.
Just need to take the time to test to find the right combination.
Britt Lindsey