This thread now makes me want to investigate more thoroughly. In my case with RPR, they subcontracted an accounting firm to handle compliance with the new tax laws- so it is my understanding that between RPR & the accountants, they will make tax calculations & payments to SAT on my behalf. But in your case, I assume you are still using a rental agency but NOT using their accounting services (to avoid the $100 a month). In that case, I think you are correct- the rental company should remit 65% (or whatever the owner share is) of the collected IVA to you so you can file with SAT.
Regarding the actual tax rate, I believe it IS correct that the tax rate for this year is 0%- the accounting firm explained to me that it is the first step in what will be (if they are correct and my memory serves) a 10-year phase-in of the new tax system. My understanding is that that any net rental profit (after all deductions) will be subject to a flat tax- I think it may be the same 16% as the IVA but not positive. BUT, they said that it will be phased in with 10% increments each year, starting at 0% in 2014. (to start compliance and avoid "sticker shock"). So this year it will be PROFIT x TAXRATE x 0%. Then next year it will be PROFIT x TAXRATE x 10%, with that last number jumping every year to 20%, 30%, etc, until it is fully implemented in 10 years.
That above part is all based on my memory & understanding from my meeting with the accountant in February, but I am going to check in again to confirm. I will post any new details/clarifications I find out. I can provide the accounting contact also if anybody wants. I was VERY pissed off when they jacked up the accounting fee to $100/month, but I've come to terms with $50 being reasonably acceptable (considering that some part of that also includes all the bill paying services). You may want to check back with your rental company to see if they too reduced their fees- as I said, RPR told me they did it partially because other rental companies dropped their rates. Hope some of this helps!