I'm also currently trying to do Tangrowth. Empoleon FB is a must for fire decks IMHO.
The main problem I can see is the Latest Tangrowth and the SF Tangrowth each are extremely versitile cards. Because of this, they have many viable combos but you have to decide on which strategy path(s) to take.
As already said by others: The SF T-Growth would be minus 40 damage/ turn (80 with the Lv.X's power) which is some phenomenal healing potential. The SF's attacks are also good but IMHO not as good as the latest.
I'm currently leaning towards the Coupling of the Arceus Tangrowth with the Sceptile that double s the energies. IF you can get Tangrowth going in this combo with the sceptile, the deck is nearly unstoppable as you should be OHKOing everything your opponent throws at you, or they will throw canon fodder putting you ahead in prizes.
Without deciding on which strategy to focus on, you run the risk of having a pokemon thick deck which is bulky to run and super inconsistent.
IMHO, Leafeon is not a great combo. It's a complete pain to get out, as is shaymin and once it's set up, its a bit useless. Your'e opponent will probably power spray the energy attach.