Abdul Hadi Pasha
Banned
Well there weren't many agreements to beginwith. The only ones seemed to have been one between Romania and Bulgaria where Bulgaria was to cede Silistra in exchange for Romanian neutrality in the war and an agreement between Bulgaria and Serbia over a border in Macedonia which seemed to have been definitely delineated (at the very least everything south of a line running from Kriva Palanka to Ohrid was definitely agreed to be Bulgarian). Neither were that vague really.
There were very vague. Boundary negotiations have to be handled over a considerable period of time by joint commissions.
Did they argue greatly over the borders other than Silistra and the pre-war Serbian-Bulgarian agreement in OTL?
Yes; they argued over all borders. Bulgaria refused to even demobilize.
Why would the Albanians attack Bulgarian forces and Bulgaria? I agree that there are almost certain to be Albanian insurgents (in fact, weren't there Albanian insurgents already who were attempting to gain independence from the Ottomans?), but in the basic line in the pre-war agreement between Serbia and Bulgaria the only area with any Albanians I can think of that would fall to Bulgarian control according to that agreement is Ohrid/Ohri and even there Albanians don't seem to have been in a majority as one figure I've seen (which I take with salt) is that by the end of the 19th century 45% of the inhabitants were Muslim which of course means they could be all Turks, all Albanians or Turks and Albanians (I think it is more likely to be the third possibility). Bulgaria looks like it would be last on the hit-list of most Albanian insurgents.
Albanian insurgents would without a doubt attack Serbia and Greece (and probably Italy since giving Italy direct control over unoccupied Albania and thus direct control over the entrance of the Adriatic seems to be the only, remotely possible way to get Italy to drop it's support of A-H's position on Albania) and each state is very likely to support a different group of insurgents. It's more likely that Serbia will end up seeing A-H's hand behind every Albanian insurgent just as how A-H saw Serbia's hand behind every south Slav insurgent/assassin (no matter how tenuous or even doubtful) - this could result in an entirely different trigger for World War I actually, or at least a slightly different unfolding of events if Franz Ferdinand is still assassinated in Sarajevo. It's also possible that some (or in a much more unlikely situation, all) of the states involved could end up replicating the conduct of Prussia, Austria and Russia with regards to Poland: they may be suspicious of each other and have open disagreements, but will have a tacit (and at times open) agreement directed against the independence of the subjugated nationality in question. If Serbia had given up the area of Macedonia promised to Bulgaria, it may be possible that Serbia and Bulgaria could well come to new agreement directed against Albanian insurgents.
One could also expect that Serbia and A-H might well come to an agreement whereby A-H end's support for Albanian insurgents in return for Serbia ending support for south slav agitators and suddenly a major fuse has been cut, but I doubt it. Can't see either one be willing to make the first move in such an arrangement (unlike say an arrangement between Serbia and Greece against insurgents that they face in common).
Insurgents are insurgents. They will necessarily fight against anyone occupying "their" territory. It seems to me that you're saying that this arrangement is going to work better than historical. I don't see how that's possible - in my opinion this will be much worse for the reasons I've already discussed.