Dilemmas

Venusaur 100% RL/SoB
Gyarados 100% B/HP
Gyarados 100% DT/Ou
Machamp 100% C/DP
Snorlax 98% L/HB

Hello guys.
They are my champs, and , i'm noob :), i need some answers.
I'm on level 34, and i want to know what pokemon i need to power up.
Since last year i wasted a lot of stardust and i don't want to do it again.
Machamp now is 2703 CP at level 35 ( i think) like my first gyarados(B/HP) and snorlax.
I don't have already power up Venusaur(only 1200-1300 CP) and the second gyarados(DT/Ou).
I don't have Tyranitar, i collected only 36 candies of Larvitar.
I have only one Dragonite with good IVS(89%) that i maxed up.

What kind of pokemon i need to have in my team? I have a lot of "defensive pokemon" but i need a good-great attackers.
I'm defending 8 gyms with 3 Vaps , 3 Gyarados, 1 Snorlax and 1 Blissey.

I really want a good Dragonite or good Tyranitar but they, for me, are really rare.

But even this pokemon, i have a good list of pokemon that i can power up; but i don't know if they are really strong or if they are only a waste of candies.
So, who better than you can help me? :)

Golem 15/14/14 RT/EQ
Gengar 14/14/15 SC/SB
Alakazam 15/15/14 C/FuS
Espeon 15/13/13 C/Fus
Exeggutor 15/12/14 ZH/SoB
Vapo 14/15/12 WG/HP

I'm waiting for your help. With the hope of finding a good Dragonite and , in the 2019, a good Tyranitar :=)
Another question: What are the gold medals used for?
Thank you for reading.