There really is no good contemporary evidence that Lee's heart was giving him trouble but, as
@E_just_E pointed out, there is contemporary evidence that the cherries were getting the better of Lee's intestines. In that respect, he was suffering much like many of his soldiers who were also eating fruit on their way to Gettysburg.
I suppose that it's possible but, to my mind, Gettysburg was vintage Lee. It just didn't work out like it had back in Virginia.
No. For one thing, less than half the Army of the Potomac had arrived by nightfall on the 1st. Secondly, if Lee had begun to move his army, it's likely that the Union cavalry would have detected him (the Confederate cavalry was not present in large enough numbers to screen the Army of Northern Virginia) and Meade could have reacted accordingly (by falling back to Pipe Creek, for example).
The Union position was no where near as formidable as Fredericksburg. In all honesty, with the information that Lee had on July 3, his plan had a chance of success. It was no doubt a gamble, but Lee rolled the dice a lot over the previous year and had met with success quite often along the way. Only in hindsight and knowing that so much went wrong, done ask ourselves how he could have thought that the assault would succeed.
Ryan