Hello,
According to Berg's Encyclopedia of Continental Army Units the 1st Pennsylvania (which you may often find referred to as "the 1st Pennsylvania Regiment of 1777 - the key words here being "Regiment" and "1777") was formed from a number of groups of 1776 veterans, including a cadre from the old 1st Continental Rifle Regiment (whose CO, Col. Edward Hand, took command of the new unit for the first four months of 1777). The 1st Continental had received green coats faced red in the last months of its existence, to go with the green hunting shirts, and it is likely that veterans wore these when they enlisted in the 1st PA.
However, according to Katcher's Uniforms of the Continental Army it appears that between January and September 1777, the new regiment was issued over 450 coats, but interestingly, no hunting shirts. What we don't know, is what the colour(s) of these coats were - I say colours, because quite often it was not possible for the State authorities to supply enough matching suits of clothing to each regiment for all the men to look the same (and quite often, the few that matched the "official" uniform went to the officers and NCOs).
A couple of deserters from the regiment in this period (Jan-Sep 1777) are recorded wearing blue coats faced white or red (blue faced red was later its official 1779 uniform, but the blue coats faced white had "1 PB" stamped on the buttons, suggesting they were made for the unit). However, a larger number of deserters appear to have worn "light" or "cloth" coloured coats - often a euphemism for undyed wool, which would be a dirty cream colour - and there were one or two wearing "dark" hunting shirts (presumably the 1776 clothing issue).
Thus, in terms of uniform, I suspect that it was like many Continental regiments of this time, namely there was no unitary appearance, but quite likely each company had a uniform of its own, which might - or more likely might not - be similar to that of the next company. What they would have done, though, is try to distribute the clothing so as to have each company look as "uniform" as possible. In other words, your tabletop unit would have a mix of coats with the odd surviving hunting shirt, and a few guys in civilian clothing to represent the new recruits who had not yet received anything, but with the figures on any base looking more or less the same, and officers/NCOs in "official" uniform.
Tactically, the 1st PA was not a rifle regiment, regardless of its cadre. It is thought that during 1776, the old 1st Continental had gradually issued muskets to the R&F, leaving only a few riflemen. Apart from the fact that Washington was not a big fan of riflemen (or certainly not a fan of having large numbers of them in his army), the tactical "norm" of the time in almost every army was to support riflemen with large numbers of musket-and-bayonet men to protect them, due to the rifle's lack of a bayonet and slower re-load time. The PA and VA regiments of 1777 (and beyond) did retain a number of riflemen, who were occasionally detached to serve in ad hoc units - eg Morgan's contingent at Saratoga - but who otherwise were just normal line infantry. I would use them as such at Brandywine.
I hope that helps; if you want more info, just ask.
RtL