There is a type of train ticket called " Seishun 18 kKippu". There is a type of train ticket called " Seishun 18 Kippu".

Just being more specific, and capitalising the whole name of the ticket

There is a train ticket called " Seishun 18 kippu"." There is a train ticket called "Seishun 18 kippu."

This is a ticket for free-to-allows for unlimited rides on JR regular trains, and one ticket can be used for five days. This ticket allows for unlimited rides on JR regular trains, and one ticket can be used for five days.

I think "unlimited rides" is the best expression here

This is a ticket for free-to-rideallows unlimited travel on JR regular JR trains, and one ticket can be used for five days. This ticket allows unlimited travel on regular JR trains, and one ticket can be used for five days.

This is a ticket forcan be used for five days as a free-to-ride on JRpass on regular JR trains, and one ticket can be used for five days. This ticket can be used for five days as a free-to-ride pass on regular JR trains.

Your sentence structure is grammatically correct but doesn't feel very natural :)

I bought thise ticket this summer. I bought the ticket this summer.

I bought this ticketone this summer. I bought one this summer.

I have two more days left, so I'd like to go decided to go to Hamamatsu tomorrow. OR I have two more days left, so I'm going to Hamamatsu tomorrow. I have two more days left, so I decided to go to Hamamatsu tomorrow. OR I have two more days left, so I'm going to Hamamatsu tomorrow.

"I'd like" is used to describe hypothetical situations or to make a polite request. Here, because you say "I'm looking forward to it", it seems that it will definitely happen so you need a future meaning "I'm going" OR a decisive verb like "to decide" in the past to confirm that you are going.

Here's thea sample picture of the ticket. Here's a sample picture of the ticket.