These questions really should be answered by your unit's doctors since they're the ones ordering it - plus each hospital has their own guidelines as to when and how much they transfuse.
This is what we do, though...
For most blood products (PRBC's, FFP, cryo) we transfuse 10-15 cc/kg - running at a rate of 5cc/kg/hr. For platelets, we also tranfuse 10-15 cc/kg but over only 15-30 minutes.
We'll give PRBC's depending on how the kid is doing and what their hematocrit is (we don't go by hemoglobin). If it's a sick baby on a vent, we'll transfuse for anything under 40. If it's an intermediate baby we'll do it for anything under 35. If the baby is a grower-feeder, we'll do it for anything under 30. And even if the baby is asymptomatic, we'll do it for under 25. Sometimes it depends though - these aren't hard and fast rules, just guidelines we tend to follow. There are things that will impact whether or not we'll give blood - if the baby is having bradys, up on the oxygen, going to surgery, etc. then we are more likely to give blood even with a borderline hematocrit. Likewise, if the baby is getting ready for discharge we might add in a reticulocyte count - and if it's high (meaning their body is working hard to produce more blood) then we'll let them go without a transfusion because we don't want to knock out the bone marrow's drive when it's in high gear.
For platelets, we transfuse for under 50,000 usually. If the baby has chronically low platelets, we'll lower the threshold to 25,000 unless there is active bleeding or the baby is going to surgery.
We'll give cryo and FFP depending on the coags - if the fibrinogen is very low we'll give these products.
We used to keep a "blood deficit" where we recorded how much blood we were drawing from a baby for labs, and when it hit 10cc/kg we'd transfuse that much PRBC's. They stopped doing this a few years ago. I wish we'd start it up again, or at least check hematocrits on babies once a week just to monitor them even if they're feeder-growers. I've seen too many babies that were white as sheets but asymptomatic...until the hematocrit dropped below 20 and suddenly we had a sick little kid on our hands!