Will mining be viable after the halving?
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.