幸せばっかり combines 幸せ (happiness) with ばっかり, a colloquial form meaning “only” or “nothing but.” In the song, it describes the dream station as a magical destination filled with happiness and nothing else, making the phrase both memorable and wonderfully hopeful.
The song keeps shouting "パーンと弾けて飛んで行け" [burst with a bang and fly away], and the "パンパンパン" around it is just the sound of popping, like balloons or fireworks. パーン is a written-out bang, a handy word to know, since Japanese uses sounds like this all the time. In between the noise, the singer makes a simple plan: "明日の朝 映画を観に行こう" [tomorrow morning, let's go see a movie], hoping for one that teaches "本当の勇気" [real courage], so that on the way home he can forget "悲しい場面" [the sad scenes] he saw up to yesterday.
Then it turns into a train ride. "発車のベルが鳴り 一つ駅を越えた" [the departure bell rang, and we passed one station], and he wonders if it all went by too fast. Someone crying waves from the platform, and the announcement for "本当のお別れ" [the real goodbye] plays. The last stop is the funny, sweet part: a polite conductor voice saying "お待たせしました。次の駅は" [thank you for waiting, the next station is] "幸せばっかりの 夢の駅－。" [the dream station, full of nothing but happiness]. お待たせしました is the exact phrase you hear on real Japanese trains and in shops, so it is worth learning. Sad goodbyes on one side, a station made only of happiness on the other, and a lot of bangs to blow the sadness away.