1 to change port, maybe the bitcoin wallet can forward from 8333 to a different port which will easily merge the new coin due to its longer Blockchain?
The problem with it is that the reference client DOES connect to nodes with non-standard ports, albeit rarely. If that happens, your whole network is gone,
2 to increase block size, if there is not much transactions the real size will be very small, this will not make much difference
Yes.
3 decrease the maturity for mining. Will this helpful to made the coin independent from bitcoin?
Yes but read the last point.
4 change the number of mined coins in each block?
Yes but read the last point.
5 if in one block I make many transactions to let the size of the block more than 1000, as I know this block will be rejected by bitcoin but acceptable by the modified coin, so after this coin,the new created coin will be independent from bitcoin and will not merge with bitcoin due to the longer bitcoin’s Blockchain
Yes. The reference client only considers the longest valid chain with the longest proof of work. Since your block violates the protocol rule for the block weight, Bitcoin reference nodes will not accept it.
However, your modified coin node's would consider the Bitcoin chain as valid, since the smaller block size does not technically violate any rules for your modified client.
The reference client considers any block reward (without transaction fee) below the current 12.5BTC as valid so Bitcoin can still take over your own Blockchain. You have to somehow modify the blocks being produced such that the blocks are only valid on your modified coin (ie. decrease the block reward).