Not sure about first times that would fit your request, you could check my journal recs and see though, I have a lot of first times mixed in there.

Here's one that's about Sam being BIG...not nessesarly too big, but worth the read:

Title: In The Place Where It Counts
Pairing/s: Sam/OFCs, Sam/OMC, Sam/Jess, Sam/Dean
Rating: NC-17
Wordcount: ~1,500
http://lazy-daze.livejournal.com/426172.html

and fisting is one of my surefire kinks, sooo....here is one, I totally thought I had more...but looking around, I only came up with this one...I'll check through some folders and see what I come up with. It may be that most of my favs are in other fandoms (I think the first fisting fic I read was a backsteet fic, or Buffy, so, yeah) (again, you might want to cruize through my recs and make sure I haven't missed anything...and check out any that have double penetration, I think you might enjoy some of them.):

fic: In the Palm of his Hand
Rating: NC-17.
Pairing: Sam/Dean
Summary: Kinky sexing. Pliant Dean. Persuasive Sam.
Warning: Fisting. Yes, I know, I know. But I made it gentle and slow and sweet. Kay?
http://plutogirl10.livejournal.com/12161.html

I know I have more somewhere...off to check.

(and it sounds like we have somewhat similar kinks,,,any recs you have, pretty please)

Mmm. Yes. Plutogirl's story is so good, and I'm totally gunna read it again.
thank you so much!

"Leave You for the Chase" and "Reflections of You" by ze_pink_lady both feature fisting. Distrubingly mind breakingly hot fisting.

http://ze-pink-lady.livejournal.com/124281.html#cutid1
http://ze-pink-lady.livejournal.com/93364.html#cutid1

OMG thank you!

http://mickeym.livejournal.com/892131.html
http://community.livejournal.com/sn_slash/1389920.html#cutid1

Mickeym's fic was so good; I remember it and I wanna read it again now that I see it.
Thank you so much!

hopefully you can access this link : I think extremely hawt and the title of the fic is My Whole, huge hand posted by Laugiana (Emilia).

http://laugiana.livejournal.com/11231.html#cutid1

omg. that killed me.
thank you for the link!

Sam/Dean rough sex recs (http://del.icio.us/ifyouweremine/Sam%2FDean%2Brough)

J2 rough sex recs (http://del.icio.us/ifyouweremine/J2%2Brough)

Sam/Dean fisting recs (http://del.icio.us/ifyouweremine/Sam%2FDean%2Bfisting)

J2 fisting recs (http://del.icio.us/ifyouweremine/J2%2Bfisting)

There’s also an excellent Sam/Jensen fisting fic here (http://ze-pink-lady.livejournal.com/93364.html?style=mine) (its sequel, which is Dean/Jensen, is here (http://ze-pink-lady.livejournal.com/108758.html?style=mine)).

You just made me oh so happy.
*hugs and twirls*

I'm a little late to the game, but sadelyrate has a priest!kink fic that has both fisting and rosaries: Fiat voluntas Tua (http://sadelyrate.livejournal.com/33568.html). It also has a short sequel Et ne nos inducas in tentationem (http://sadelyrate.livejournal.com/37071.html).

This one's rather dark but quite original - Personification by ruefulgirl - http://ruefulgirl.livejournal.com/732.html