First off, to your question about the forum, it's pretty much dead since GLU stopped updates and weekly content for Clan Wars, Global and League events. Some still hold hope for the new studio to return these as well as new regions, many have given up.
As to buying secondaries, these will always require gold for purchase. The tesla can be effective for at least 2 tiers of PvP increases, but not the tesla mission levels beyond your current region, 7.0 - Brazil. You will be able to play those tesla regions 12 times to pocket increasing diamond amounts, as well as all previous tier levels. My recommendation would be to wait and buy the x8.0 tesla offered when you do the next region's - Kill Club first tesla mission, as these are half the cost of the ones offered in the store.
Now for a shameless plug if you're an Android player, I can give you more info if you join ONEWORLD. I'm still active, and hopeful the game will continue.
Nope...the TESLA you purchase maybe useful for the next 2-3 levels...after that it'll not be that effective. As your level goes up, your Opponents will be hard to kill with the gun you purchased on a lower level.
Moreover since GLU has stopped Global event, the only option is to play Campaign accumulate gold and purchase guns or real money (not recommended as the future of the Game is unsure).
Answers
As to buying secondaries, these will always require gold for purchase. The tesla can be effective for at least 2 tiers of PvP increases, but not the tesla mission levels beyond your current region, 7.0 - Brazil. You will be able to play those tesla regions 12 times to pocket increasing diamond amounts, as well as all previous tier levels.
My recommendation would be to wait and buy the x8.0 tesla offered when you do the next region's - Kill Club first tesla mission, as these are half the cost of the ones offered in the store.
Now for a shameless plug if you're an Android player, I can give you more info if you join ONEWORLD. I'm still active, and hopeful the game will continue.
Moreover since GLU has stopped Global event, the only option is to play Campaign accumulate gold and purchase guns or real money (not recommended as the future of the Game is unsure).