There is already a subpoena that Trump is fighting to get his financial records from Deutsche Bank and his tax records are part of that. Then there was that NY State investigation looking at his state tax records. That is also tied up in the courts which is Trump's modus operandi.
There is still one of the emoluments cases in the courts. They weren't both stalled under a no standing charge. So no need to add that to the impeachment. The Brookings panel this morning thought the emoluments issue was weak in terms of impeachment. Take a look at the link to that panel discussion in my post upthread. You can click on any segment in the transcript and that part of the discussion will play.
One of the issues they pointed out is too many subpoenas and you risk Trump tying it up in the courts until after the election. While that may seem OK, think about it, do we want Pence for half a year or four years?