Ηοw many fighters you think that Russia needs? I think about 1000
It is hard to say, if they get 250 PAK FAs (eventually), then about 100 Su-35s and lets say another 150 Su-30s/Su-27SM2, then we have 500 odd Sukhois, which is a good start. AFAIK the plans are for 50 odd Mig-29M2/35, and perhaps 100 Mig-29SMT upgrades of which they already have about 30 odd, and if you add 100 Mig-31s that are to be upgraded by 2020 at a bare minimum, and perhaps add another 150 that wont be upgraded but still might be available for use and perhaps 200 Su-27s and Mig-29s with minor upgrades that still might be in service and we end up with about 1,100 aircraft, but of course the numbers of old model Flankers and Fulcrums will decline fairly rapidly.
The Russian AF has an enormous area to cover, but with a 1 million man armed force they can't afford to have thousands of aircraft any more.
Fortunately for them the improvement in electronics and technology will allow a significant overlap in performance, so instead of having a Mig-27M ground attack unit and a Mig-23 fighter group, they can have a Mig-29M2 air group that can engage air and ground targets much more effectively than either of the older dedicated aircraft could manage thanks to new multi mode radars and sophisticated modern guided weaponry.
Will Mig-35 be single seater or two seater?
The Mig-29M2 and Mig-35 share the same aircraft structure, though with some fairly significant differences in terms of wing wiring and the location of sensors and avionics. The Mig-35 has the same long canopy that allows for single and two seat arrangements.
Single seater Su-35 and Mig-35 would be dedicated air to air fighers, two seater Mig-29M2 and Su-30SM could be more multirole fighters, better suited for ground attack and SEAD missions because of second operator in back seat.
Actually two seat '35s would offer operational training options while at the same time offering light strike, air command and other roles where the front seater focuses on flying the mission and the back seater can concentrate on other things... incredibly useful when things get busy...
Of course the 5th gen avionics should be able to minimise the pilots work load by only showing pertinent information... in the middle of a dog fight the pilot does not need to know that the oil levels have dropped by a few litres since they took off an hour ago for instance. If however the oil is dropping rapidly and needs attention then it might be something that either needs automatic attention or the pilots attention to prevent the aircraft dropping from the sky.
Two seater for the MIG 35D only not the MIG 35.
So what you are saying is that the Mig-35D is the two seat Mig-35?
I rather suspect they have changed from the tradition UB to denote the fact that the new aircraft is fully operational rather than a reduced range radarless training aircraft. Perhaps D for double as in two seat?
The Mig-29K2, Mig-29M2, and Mig-35 all share the same airframe/cockpit design which allows single seat or two seat arrangements without reducing fuel or changing the length of the aircraft or removing radars to compensate for the weight change.
Very simply the aircraft was designed with the second pilot in mind. When that pilot is not there (ie in a single seat configuration) that area is used for fuel and other bits and pieces.