1st Deal-Help! In Need of Some Advice!

Hi!

I have a seller with a 3b/2.5b home (1586 sq.ft.). The home doesn't need any major repairs, so I am not sure what to put down for rehab. Is 5K too low? or should I just go by the sq. ft. and say 15k even though I doubt the home needs that much work? Another question is that the seller said he would walk away from the home if I could get a cash buyer for 200k. The problem is that the ARV is $200k! so this leaves no "skin in the game" for my buyer or even an assignment fee! In addition, the seller owes $140k on the home and has an assumable mortgage of $65k. Not sure if I should bother with this. I could really use some advice. To do the deal at 70% I would have to get the seller down to 140k right? Would it be possible to offer the seller $150k and this be still a viable deal that I can market to my buyers? Thank you for any help with this! As you can see, I am a newbie!