I’m sure this has all been covered in one way or another. Honestly I stopped reading replies after the 2nd page. To answer your cash vs leverage question I think it depends on the property, the location, your goals, and your situation.
This may sound crazy but IMHO the person who uses all of his/her cash to buy 1 property all cash is in just as much trouble if something happens requiring major repairs as the person who over-leverages themselves and then tenants stop paying rent.
I think it's wise to do the math on a property as if you intended to leverage at 80%. This way, even if you pay cash or use less leverage, you have available equity should the need arise without turning your cash flow negative. An easy way to see how much an all cash model will hinder your growth is to divide the cash you would retain with financing by the P/I portion of your payment. For example, let's say you have $100k in capital and you finance a $100k house at 80% LTV and 6% interest (conservative investment based 30 yr note) the loan will cost you $400/month in principal and interest. If you divide the $80by $400 you will find that it would take you 16.67 years prior to inflation to recapture that $80k.
Assuming a $200/mo per property cash flow after PITI, PM, and 15% additional hold-backs you could hold back $20k for initial reserves and buy 3 more like properties tripling achieving the same cash flow as if you had paid cash for 1 property while cutting your risk of tenant default by 65%.
Additionally, if you only managed to negotiate a 20% discount on the properties you purchased you would have gained an additional equity value of $40k in the first year.