Hey TienDow, welcome to the forums!

Diplomacy is at a VERY early stage in development at the moment; Mike has lots of plans for changing and improving it. If you notice any bugs with diplomacy, then it's usually best to ignore them.
The sending resources bug is a known issue; some of the messages in the game files aren't written in the correct order so the game uses the wrong ones. It's something I told Mike about a long time ago actually, so it may be he forgot about this one. I'll give him another nudge about it.
Dilithium isn't currently used (Much) by the ships; it is a relatively new resource in the game and I haven't had a chance to update all the ships with their correct Dilithium build-requirements. So there isn't anything wrong with your Dilithium pool, you just don't need it yet so it doesn't go down.
Credits are needed for maintaining your fleets and paying for build rate incrases of current projects. But that feature isn't in the game yet, so they're only used to pay for maintaining your fleets. Try building more ships than your empire can support. If your credit stockpile doesn't start going down even though you're losing money then that's a bug.
_________________"Anyone without a sense of humour is truly at the mercy of the rest of us."

