Kirk did have the most costume changes because he was the lead character, and Shatner the lead star. Spock would probably be a close second in terms of costume changes.
Middy:
I think you may be correct. Let's review:
Spock:
-Three uniforms in the series (blue ribbed collar tunic in
The Cage; golden ribbed collar tunic in
Where No Man Has Gone Before; blue tunic with black collar for the rest of the series);
-Four uniforms in the movies (gray tunic/pants, with gray-blue "dickie"; tan/brown landing party jacket (TMP); burgundy duty uniform with white turtleneck under jacket; tan commando outift (TWOK on, TFF).
So looks like seven all together, or about half the number of Kirk's outfit. Now, all the cast's totals would be higher if we counted stuff like spacesuits and a couple of times, Spock wore the blue jumpsuit enlisted folks wore while in sick bay.
As long as we're counting Spock's, let's look at the rest of the main cast:
McCoy:
-Two uniforms in the series (blue tunic with black collar; blue short-sleeved tunic over black T-shirt);
-Seven uniforms in the movies (gray tunic/pants with v-neck and lapels; white medical togs/jumpsuit; tan landing party jacket (TMP); burgundy jacket/greenish turtleneck/black uniform pants; burgundy landing party coat/greenish turtleneck/black uniform pants; white medical togs/jumpsuit with greenish turtleneck underneath; tan commando outfit (TWOK on).
Total: 9
Scotty:
-Two uniforms in the series (golden tunic with ribbed collar in
Where No Man Has Gone Before; red tunic with black collar);
- Six uniforms in the movies (gray tunic/pants; white engineer's outfit (TMP); burgundy jacket/gold turtleneck/black pants; white engineer's outfit with additional accoutrements; alternate duty burgundy jacket with lapels/gold turtleneck/black pants; white turtleneck/black jacket/black pants (TWOK on).)
Total: 8.
Sulu:
-Two uniforms in the series (blue ribbed tunic collar in
Where No Man Has Gone Before; golden tunic with black collar, rest of the series.)
-Five uniforms in the movies (golden "leisure suit" uniform; golden tunic/pants; white short-sleeved top/golden pants (TMP); burgundy jacket/gold turtleneck/black pants; beige commando outfit (TWOK, TSFT, TFF); burgundy jacket/white turtleneck/black pants (TUC).)
Total: 7.
Uhura:
-Two uniforms in the series (golden dress/uniform; red dress/uniform);
-Five uniforms in the movies (golden tunic/pants; ; white short-sleeved top/golden pants (TMP); burgundy jacket/blue-gray turtleneck/black pants; burgundy jacket/blue-gray turtleneck/black skirt; beige commando outfit (TWOK, et al.).
Total: 7.
Chekov:
-One uniform in the series (golden uniform tunic);
-Three uniforms in the movies (golden tunic/pants (TMP); burgundy jacket/blue-gray turtleneck/black pants (TWOK on)).
Total: 3.
So, Kirk has the most (14), followed by McCoy (9), Scotty (8), with Spock, Sulu, and Uhura tied with 7, and Chekov bringing up the rear wtih 3.
Red Ranger
