I have a few questions in how to start the offer/negotiation and listed the basic details of the property below.How would you structure a seller-financed deal?

Just open escrow and close as normal.. title company will send for a reinstatement figure you put your downpayment they reinstate for you all is good.Not sure if this will trigger the Alienation clause or not.. technically it does but that's at lenders discretion. 

Based on the details above, we would love to understand people's point of views on if this is a good deal or not and/or something that we should undertake. 

Your question is just too broad to get a more detail answer IMHO. 

My question is if my mortgage on the property is say 350 and it's renting for 550 won't I technically be negatively cash-flowing due to the probability that the 40% cushion initially factored into the deal will probably cause me to have to put a small amount of money in monthly?

Shoot me an email with some more details.

If I waited until end of 2019, I could afford more.I will message you for the lender's details.

I might of got a little confused now that I read @Nicholas Horsburgh his reply he did not say PPM he said offering memorandum .. many would take that as a PPM  ( private placement memorandum) but maybe he meant like a detailed description in writing of what your trying to accomplish.Generally there are no real contracts for loans there are loan documents though Note  mortgage settlement statement and depending on the lender a whole host of other various and sundry documents usually disclosures so you can't sue the lender. :)

Good for you that your taking the plunge into this big, detailed world of real estate!

I'll spare you the details, but the houses generate enough rent in the first 12 months or less to cover the purchase price.