The Mig-35 could probably go into production in 2014 and they will probably buy about 50 or 70 in total, and that would be good for Mig as they would get production experience, and be able to test new stuff.
I really don't think less than 100 Mig-35s will be able to replace the thousands of single engined fighter bombers that they have lost.
I agree that for now making a 5th gen light fighter doesn't make sense and the question should be looked at again in about 2016 or so with a view to the new aircraft entering service in 2022-2025. At that time they will have PAK FA in service in numbers and most of their legasy aircraft (Mig-29s, Su-27s, Mig-31s) that haven't been upgraded will need to be scrapped and replaced.
The Su-35, Mig-35, and Su-34 will be formidable support aircraft for the PAK FA, but I also think that by the 2020s that NATO will have more stealth fighters (F-35s) than the number of PAK FAs that Russia could afford could deal with.
I think the Su-35 will be a very capable opponent for the F-35, and in many areas will be superior, but by 2020 I would hope that Russian aircraft technology will have reached a level where it was ready to make a genuine light 5th gen fighter that is affordable and able to foot it with the best.
It will be a practical aircraft that while perhaps not cheap to buy will be cheap to operate and effective for all those bomb truck roles you would never risk a PAK FA for.
A small light 5th gen fighter could be used as a light recon aircraft, precision attack, fighter, jammer... the number of roles it will be able to perform will be broad.
In many ways it will be a stealthy F-16... in the USAF when F-15C fighters are available the F-16 is a bomb truck. For European AFs that have F-16s as their only fighter it is fighter and bomb truck and everything else.
At this point, ordering Su-35 would probably be cheaper.
Not in the long term.
In most of western Russia most Su-27s operate with 3/4ths empty fuel tanks, which is a bit like using an An-124 to deliver 6 tons of post. For many units a Mig-29 sized aircraft is a more efficient choice, and having an alternative to a Sukhoi fighter is good for competition.
An official... I think it was Rogozin said recently that competition for the PAK FA now would make Sukhoi work harder and result in a better product. Obviously there is no domestic competition for PAK FA now and there wont be... the Mig light 5th gen fighter will compliment rather than compete.
It would also make rather more sense using Mig-35s in support of Army units through frontal aviation than to use Su-35s.
The Mig-35 would be more suited to frontal aviation units than the Su-35, the latter would be more useful for air superiority missions over much larger areas.
...BTW it would be cheaper to only buy Mi-28s, but it would not be better.