I really want to use blockchain tools effectively and provide decent quality and earnings for both parties.
Imho you have to properly ask yourself what you need blockchain for and how you expect this system work. Maybe express your ideas so we don't have to guess.
I'll write down some basics/ideas I think they may be helpful for you.
While it can be great for tracking the history of a task, it will be slower than a traditional DB. And editing existing entries will probably not be possible in na simple way.
Then you have to think it over who will mine that blockchain, since without a proper reward nobody moves a finger and a proper reward for miners may mean less reward for the actual freelancers, which is not good.
And if you want centralized, internal "blockchain", imho you better go for an old school DB.
Then the payments. If you want to allow payments in crypto, you don't have to make your blockchain, instead wallets of the actual most proeminent cryptocurrencies will do.
All you have to do is to setup properly the wallets in your system to allow you act as an escrow in case of problems (2-of-3 multisig wallets may do).
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All in all, I have the feeling you want to attract some funds by calling this "blockchain project", although the key features most probably don't need blockchain. But maybe I'm wrong.