Moreover isn't the word you are after. It implies a relationship between the two ideas; moreover, it implies that the second is even more pertinent to what you are discussing than the first is.
On the other hand (not in the other hand) isn't an appropriate phrase either. It too implies a relationship, specifically that the two ideas are somehow opposite to each other in some sense. For example, I could have a burger and chips for lunch today. On the other hand, I could be good and have a salad instead.
The word you are after is probably "also", as in "I would also like to see if you could help me with my income tax declaration." However, you still hit the basic problem that the two sentences are not actually related to each other. They don't belong in the same paragraph, since part of the point of a paragraph is that it collects one idea together. If you try to jam an unrelated idea in like this, a lot of people will simply fail to notice it.
So a better way to structure your email would be something like this:
Hello. [This is rather abrupt; a bit more of a greeting wouldn't hurt.]
I can start working on the project, just tell me what the requirements are. [It would help to put in something relevant to the project here, just to fill out the paragraph, even if the person you are writing to doesn't need to know. Something that's too terse comes across as impolite.]
I would also like to see if you can help me with my income tax declaration. [Again, padding it out a bit with a reason helps to make it sound more polite.]