after Genesis of Bitcoin, ie creating block#0, every wallet owner has an empty wallet, by the way there is nothing to mine. So how the block chain process can be initiated?
All you need in order to mine is a block to mine on top of. There don't need to be new transactions for mining to be possible. An empty block can be mined as easily as one with transactions in it. And, of course, there's always the transaction to pay the reward to the miner, at least until the block reward drops to zero.
Are there Happy Hours and some lucky people are elected so that they can get free bitcoins? is it called premined bitcoins? In other words, where I can find description of the bitcoin blockchain bootstrap?
No. The only way new bitcoins can be created is by mining.
As an alternative question, is it possible that bootstrap process initiates on a credit/debt basis, ie ledger balance always nul?
No. Bitcoins just exist and aren't an obligation or debt of anyone or anythinng else.
Thinking of bitcoin mining as analogous to gold mining may help. If you have an ounce of gold, nobody loaned it to you or owes it to you, you just have it. And all the gold that will ever exist is already somewhere, it's just not accessible yet. And when someone finds some gold, it transitions from being unowned to owned and the amount that is still left to be mined goes down.