search around the forum for perry discussions, most people have a hard time with regular sweet pears since almost all the flavor tends to ferment out, and true perry varieties are pretty much unheard of outside england's perry country (herefordshire, worcestershire). i would avoid adding any water, the last thing you want is to dilute out the flavor any further, and taste when it's about done fermenting. you might find that it lacks any acid (hence the suggestions above), pears don't pack the malic punch that apples do. i have only made one perry, from slightly bitter cooking pears, so i am by no means an expert, just pears + champ yeast, and mine was so bad that i had to really struggle to keep myself from tossing it down the drain, after 10+ months it has come around a little bit but is by no means delicious. (made an ok vinegar though). if it comes out like mine then maybe an apple/pear blend is in order
also bear in mind that pears usually have some unfermentable sugars so will finish a bit higher than apples. for me pectic wasn't necessary, i don't think they are nearly as pectin rich as apples but not 100% sure. leave out the star-san- what's the point?