Can i trust on etherium project
I want to hold it for long term 5-10 years
You can trust, ETH is managed by professional people and they know the tech. Ethereum is number 2 on CMC for that reason.
When HODLing I would check the price at least every month and when you notice it's going to a new ATH then sell it.
Can i use hardware wallet (ledger or trezor)?
Yes, Hardware wallet works, but it is very expensive. MEW is also fine if you are carefully when creating the wallet, MEW has also good security.
Good Luck bro
I think that it is possible to combine these two answers in one and say that ethereum is even a much better choice for investment than Bitcoin today, and its best to store it in MEW, because Although it is an online wallet, its security depends only from the user himself. In other words, if the user does not make a mistake, then his funds will all be safe.
MEW can also be run offline so no need to do it online because offline is always more secure. You can read a nice tuorial here to do it really offline and no risk to get insecured wallets. Read here bro:
And why should I respond two questions in one? Brings more explanation for OP when he asks two questions, gets 2 answers.