Will mining be viable after the halving? So I don't understand the halving very well, will miners just make half as much? Will the price double or the difficulty change? Will bitcoin mining just become so hard it ceases to be cost effective? Am I making a mistake getting into bitcoin mining? Will people just switch to a altcoin?
The block subsidy, i.e. the amount of newly created bitcoins per block, will half. Transaction fees are not affected by the halving. The exchange price of Bitcoin is up to market mechanisms. The halving doesn't change the difficulty. So, yes, probably the value of the mining reward will drop significantly between block 419,999 and 420,000.
Mining already is infeasible at home. 
Yes, you're making a mistake getting into Bitcoin mining. 
Personally, I doubt that any altcoin will be successful.