how hard is it to be a pi phi/ theta/ kappa

Getting recommendations is extremely important! They don't make it sound like it is, but it definitely matters a lot. But, don't go into rush with expectations like this. That is such a toxic way to enter recruitment! Just go in with a fresh mind and no expectations, and you'll be happy where you end up. Sometimes you can think you're the perfect candidate for a sorority and they'll still cut you, so don't get your hopes up. The best advice I can give you is put in the effort not to just get into a top sorority, but just so you can extend your chances to get into any house that wants you. Good luck!

What she said

Even though people rank pi phi, theta and kappa differently, I would say they're 3 very similar sororities in terms of type of girls they're looking for.
It sounds like you're well prepared!! If you're worried about "being a little bit bigger", just focus on dressing yourself well!! This doesn't mean expensive outfits, just outfits that are flattering for your body type and show your style.
I agree with the comment above, if you're so successful in so many organizations it'll stand out on your recs so just make sure your recs are all good!

Go on in and keep humble bragging.
You think you’re awesome & you think you deserve what you perceive is a top house.
The thing that will keep you out of any house is the size of your ego.