Kintetsu railpass related questions

How much does it cost to get additional limited express tickets, if i already had used all the 3 included tickets? For example, between Nagoya-Kyoto? Also, if i don't buy those extra tickets - does it mean that i have to use the Kintetsu trains, which are much slower when compared to the fastest Kintetsu ones?

How much does it cost to get additional limited express tickets, if i already had used all the 3 included tickets?

It depends on the distance traveled.

For example, between Nagoya-Kyoto?

1850 yen. This assumes that your transfer time at Yamato-Yagi station (where you have transfer trains) is less than 30 minutes. If the transfer time is more than 30 minutes, you have to buy two separate limited express supplements, which will add up to 2430 yen.

Also, if i don't buy those extra tickets - does it mean that i have to use the Kintetsu trains, which are much slower when compared to the fastest Kintetsu ones?

For example, to get from Kyoto to Nagoya by Kintetsu limited express takes about three hours (typically one transfer of trains along the way). By express trains it takes about 45 minutes longer (typically two transfers along the way).