Due to absences I usually GMed act 1 to three players and , assuming PB 15 and no druid/summoner, most encounters was on the edge. I strongly advise to use helpful NPC to "join" PCs . Especially water encounters favors quantity over quality due to very harsh water combat rules.
Well after looking around all my friends, it seems like we're only going to start out with three players and myself. I got a few options. I just want to see what would be best
1. Make a dedicated DMPC/NPC and just play it in a reserved manner, being rather secondary to the other PCs (like not making major decisions and whatnot)
2. just run it with 3 PCs.
So I got a question, is this viable for 3 players? Would I need to have them enter adventures one level higher, or could they last at normal level with three people?
We did it with four - admittedly optimized and well-played - and while it was challenging it was never miserable and we lost non of the PC's.
My advice is be on the lookout for potential allies to join the team. Our group had Sandara for the first three books and the last one, had Rosie for the first two books before she went off on her own (but made reappearances), had a Tengu Barbarian with them for a while and even got some timely aid from a leveled up Mardus Siggs. There should always be at least 1 'DM's PC to balance things out and act as your mouthpiece to guide or lead astray. Also, established NPC alliances and relationships create wonderful opportunities to offer help when needed, be in need themselves or add poignancy to a scene when they are killed.
Also, don't neglect your crew - with 20-40 pirates aboard ship there should always be plenty of redshirts available to step up and take one for the team.