My question is - is Lightning Network really going to lock our funds for so long time that its going to cause problems?
No, it is not. When you "lock" your funds in a LN payment channel, you can still spend those coins, albeit only with the other party in the channel. However with LN, if that other party is connected to other people via payment channels, you can make payments to those other people and the people they are connected to and so on and so forth. So your funds aren't "locked"; you can still spend them and move coins to other people that have LN channels open. Furthermore you can choose to close a channel at any time that you want and be able to access your coins as soon as the channel closing transaction confirms. There is no set time limit on a channel and there is no minimum time required for a channel to be opened.
Cause it seems to me obvious that hackers could fail transactions for purpose and block the network.
What do you mean by "fail transactions"?
The lightning network is different from DASH and IOTA in that it itself is Bitcoin, not an altcoin. With LN, you are moving and using Bitcoin so the value you move is fixed and does not change. If you were to use an altcoin in the same manner, you would risk losing money as the altcoin's value compared to Bitcoin's changes. Furthermore, many of the security risks and potential attack vectors are fairly well known because LN uses Bitcoin and Bitcoin's security risks and potential attack vectors are well known. With an altcoin that uses some crazy cryptography that may not necessarily be secure (IOTA had some broken cryptography which were pointed out in a security review done by 3 MIT DCI researchers) does not have known security risks and potential attack vectors.