A couple of questions about custom feats

[Teaboar]

I'm curious if Northern Hewing + Athkatlan Triparite + Combat Expertise + Flurry of Blows can all be active at the same time (and whether they actually work together).

I'm also wondering if Chiontar Seagull can basically guarantee a hit against any monster if my tumble is high enough? If it can then how high would my tumble have to be to make it reliable?

[KOPOJIbPAKOB]

There can be only one combat mode active at the same time and one custom combat style. So basically, NH doesn't stack with AT, and CE doesn't stack with FoB, but NH stacks with CE or FoB for example. No idea about CS.

[Rudolph]

It's (Northlander Hewing OR Athkatlan Triparte) AND (Combat Expertise OR Flurry)

[Teaboar]

Thank you for the quick replies. That helps a lot.

Does anyone have experience with the Chiontar Seagull skill? I'm still curious about that one.

EDIT: I have another unrelated question. I was wondering how does the Ranger feat 'Improved Favored Enemy' stack? I know it stacks with favored enemy, but does it also stack with other Improved Favored Enemy feats? If I have for example 5 FA feats and 2 IFA feats, would I do 5+3 extra damage to my favored enemy, or would I do 5+3*2 damage to my favored enemy?

EDIT2: More questions... If I have Sembian Fencing and Greater Flurry active at the same time, will I have 2 attacks per round or 4 attacks per round?