I kinda lost my way towards end of draft and drafted bunch of rookies. Is it overkill?
The league is has a small hitting lineup so didn't want to fill my bench with hitters but pitching wise it was shallow so I started drafting rookies.
My pitching staff is a bit weak but I am very happy with my hitting.

16 team yahoo redraft. 6x5 Roto (OBP is extra hitting category)

C. Alex Avila
1B. Joey Votto
2B. Emilio Bonifacio
3B. Adrian Beltre
SS. Josh Rutledge
OF. Adam Jones
OF. Shin-Soo Choo
OF. Alex Gordon
Util. Paul Goldschmidt
BN. Brett Wallace

SP. Jordan Zimmermann, Jeff Samardzija, Phil Hughes, Tommy Milone, Mike Fiers, Felix Doubront
RP. Tom Wilhelmsen, Greg Holland, Ryan Cook, Sean Marshall

Travis d'Arnaud
Matt Adams
Dylan Bundy
Shelby Miller

I think you'll be fine with Miller and Bundy. I think Bundy'll be up some time in June and Miller probably is the #5 in St. Louis right now.

Adams, though, will need an injury to occur to get playing time. D'arnaud is the most interesting one. He could make the roster, but I think the Mets may want to delay his service time.

With all of that said, I think you did reasonably well. Miller and Bundy may make it for you.