question about counters
 

for counters, if i were to say 20 days, do i use hatsuka or nijuunichi


for stuff like shirts, if there are more than 10 (15) do i go juugo mai

20 days, 20th day of the month = はつか

For shirts, the counter is 枚（まい） regardless of the quantity.

if 1 month is ikagetsu will 11 months be juu ikagetsu or juuichi kagetsu?

Think of the っ being a function of two sounds bordering each other, not two words bordering each other.

It's not that いち and ヶ月 are next to each other. It's that ち and ヶ are next to each other.

じゅういっかげつ

oic, k thanks for the replies