Didn't edward iv leave his brother Richard in lots of financial difficulties though?

No, he did not. I really don't know where this myth has originated from other than the persistent need to victimize Richard.

Firstly, Edward IV didn't leave Richard anything. Whatever he left was for his own son and heir, Richard's nephew, who Richard usurped.

Secondly, Edward IV was the first king since Henry II in 1189 to die solvent. He had managed to break the vicious cycle of plummeting debt and inefficiency that had plagued pretty much every single ruler till then. It doesn't really matter how much money the crown actually had left at the time of his death*, because the fact that he died solvent meant that whoever his successor was (in this case, Richard III), they were going to begin their reign with a financial advantage that no English monarch had enjoyed for the past 200 years. I don't know Richard's fans have convinced themselves that he inherited financial difficulties instead.

As stated by David Horspool, Richard's own historian:

"(Richard III) would try to differentiate himself from his brother, whose ‘unlawful invencions and inordinate covetise, ayenst the lawe of this roialme’ he would later denounce in an Act of Parliament. In fact Edward had managed to set royal finances back on an even keel after the disastrous waste and inefficiency of Henry VI (and all former kings post Henry II), Richard was, initially, the beneficiary of the better practise instituted by Edward IV.”

(The contemporary Croyland Chronicle mentions a main reason that Richard was better prepared to defend his kingship was "because of the treasure which he had in hand—since what King Edward had left behind had not yet all been consumed". They may have exaggerated the money Edward left behind, but either way it shows how contemporaries were aware of Richard's comparative advantages. It's highly ironic that what should have been used to uphold Edward's son was now being used to uphold his son's usurper instead).

Thirdly, Edward IV had presided over a highly effective and innovative combination of financial policies. These included the elevation/increase of royal chamber finance, the enlargement of the crown lands (Steven Gunn calls it "the most extensive royal demesne in medieval English History"), and an increase in royal feudal rights towards the end of his reign, among others**. Most importantly of all, he was actually successful, meaning that whoever followed him would have the huge benefit of having his established and well-attested precedent to continue from. Indeed, Charles Ross has noted how "Henry VII had the great advantage of being able to build upon the foundations laid by his father-in-law". Richard III, who seized the throne just a few months later, would have had the same advantages, as Horspool also notes.

Richard III, in fact, seems to have (temporarily) reversed some of his brother's well-established policies which could be used to gain money. Eg: he abolished benevolences; and he repealed Edward IV's newly established wardships and marriages act in the Duchy of Lancaster "notwithstanding that he conceiveth the said act to be to his great profit … having more affection to the common weal of this his realm and of his subjects than to his own singular profit". If you deliberately reverse policies with immense potential for revenue-raising, I don't know how you can then go on to complain that your brother left you nothing.

In conclusion: no, Edward IV did not leave Richard in financial difficulties. If anything, he left Richard with financial advantages that no king had had in over 200 years.

(Also, just to clarify: the Woodvilles did not steal the treasury. We know for a fact that Elizabeth Woodville did not have any money in sanctuary. The story of a theft was only mentioned by Mancini and either originated in gossip or, more likely, from Ricardian propaganda aiming to vilify them in 1483 by positioning them against the crown.)

*We know for a fact that Edward IV died solvent, but from what I understand, the exact money he had is impossible to know because of his missing chamber records. Contemporaries like Croyland did believe he had substantial money and treasure; on the other hand, Rosemary Horrox has analyzed how his cash reserves were probably relatively low due to international conflicts the previous two years. Either way, like I said, the main thing is that he was the first king in over 200 years to die solvent, which was massively advantageous to his successor. **While his policies were clearly innovative, they weren't all completely original. However, their combination certainly was; they were modified to actually work better; and they were initiated from the beginning of his first/second reign and widespread across the royal lands (rather than in smaller pockets), meaning that they were clear systematic policies. They were also, like I mentioned, actually successful - meaning that they would be the proven precedent that his successors would turn to.