Welcome to the forum! We're glad you're here! Did you post some pics yet?
What engine do you have? How long did the engine sit?
I would start with a compression check, first to make sure all cylinders are good. Also, are you sure all cylinders are firing?
If its a V8, the rear main seal is pretty easy to replace and they're cheap. I got nothing on your flexplate though.
2011 Nissan Pathfinder Silver Edition 4x4
2009 Mazdaspeed3 Grand Touring
1999 VW Cabrio (my daugther's to drive, mine to maintain)
1979 Jeep Cherokee Chief Wide Track, 401, bone stock