Dutch Pinnace: If HP remains the same, I suggest lowering the HP for the vanilla model of the Pinnace, and also for the Merchant Pinnace, in order to be consistent with the Pinnace line.
Caravela Redonda: I think your solution would be the best for it.
Merchant Pinnace: capacity 5000, armament 26 guns of 9lb, crew 120, HP 3500, price 51200, speed 8.5/12.6, turn 60/29
Medium Pinnace: capacity 3500, armament 18 guns of 9lb, crew 117, HP 2300, price 54800, speed 9.5/12.6, turn 60/29
Vanilla Pinnace: capacity 5000, armament 24 guns of 9lb, crew 108, HP 3500, price 51200, speed 9.0/12.6, turn 60/29
Dutch Pinnace: capacity 3000, armament 26 guns of 9lb, crew 117, HP 2300, price 54800, speed 9.0/12.6, turn 60/29
So the Merchant Pinnace has a couple more guns, crew to man them, and is a bit slower. The Medium Pinnace is the fastest of the lot, and the lightest armed. The Dutch Pinnace is the heaviest armed, losing some cargo capacity to make room for the guns. And whoever added the new pinnaces forgot to change the arcade speeds to match the realistic speed, so I'll correct that - Merchant to 12.1, Medium to 13.1, the others stay as they are. Otherwise, all ships are not created equal! If you're buying, you take whatever the shipyard has on offer or wait to find the type of your choice. If you're capturing one for your own use, the same applies - take what you can find, or dump it and wait for the one of your choice.
Incidentally, those armament values don't tell the whole story. The Medium Pinnace doesn't have much of a broadside because four of its guns are on the stern, while the Vanilla Pinnace has six guns on the stern, very nasty for anyone trying to chase it! The Dutch Pinnace has the heaviest broadside of the lot, but only two stern guns.
USS Enterprise: I think it's best to drop it at Tier 6, with its stats also balanced for that tier. But you can choose whatever you think it's best.
Tier is based purely on the base crew number as given in "Ships_init.c" without national modifiers or randomising, which means dropping its crew to 65 will indeed put into tier 6 - just! Tier 6 is crew less than 100, greater than or equal to 60.
European Barque: So you mean you are going to reduce their stats to be similar to the English Bark? That could probably cause that players would stick more with luggers because of their better speed. Why do you think it is necessary to reduce their speed? (Besides balancing with "Realistic" speed of course).
The entire reason is to balance it with realistic speed so that comparisons between ships should be similar regardless of which setting you use - if ship A is faster than ship B in realistic mode then it should also be faster in arcade mode. (There are probably more which need their arcade speeds adjusted but I haven't the time to check the whole lot!)
In any case, personally I tend to stick with the lugger for speed, turn rate, and the superior ability to sail across the wind. Then I'll take full advantage of that agility to zigzag across the stern of something bigger and pound it with grapeshot until it surrenders. Forget barques, I'm after something bigger!
If you want, I can include all the changes you will do to the ships' stats that you mentioned. If you share with me the specific changes, I can include them for the next release.
European Barque: arcade speed changed from 14.9 to 11.9, Jackass Barque arcade speed changed from 15.3 to 13.3, English Barque (New Horizons) arcade speed changed from 14.9 to 12.7, Barque Longue arcade speed changed from 15.6 to 13.6.
Heavy Brig (New Horizons): HP changed from 3500 to 2500.
Dutch Pinnace: arcade speed changed from 12.6 to 12.0.
Fast Galleon: arcade speed changed from 12.5 to 13.5.
American Brig (USS Enterprise): crew changed from 144 to 65 (which drops it from tier 5 to tier 6).
East Indiaman: arcade turn rate changed from 30 to 32.
Treasure Galleon: arcade speed changed from 8.0 to 9.5.
Armed Schooner arcade speed changed from 14.5 to 15.5, arcade turn rate changed from 38 to 50. Corsair Schooner arcade speed changed from 14.3 to 15.5, arcade turn rate changed from 35 to 50.
Caravela Redonda: Spanish Main period chance changed from 0.6 to 0.4. This probably doesn't affect your guide, it just means this antiquated ship becomes less visible in the early 17th century.