If Ukraine had access to planes do they have or are pilots being trained to fly these planes in battle. How long does it take to train a pilot?
Ukraine certainly has an air force that includes fighter jets. I have no idea how capable they are.
Also, most (all?) of their planes are Russian made and I doubt Russia is sending them new spare parts. Such planes take a great deal of maintenance. While Ukraine probably has some spare parts in stock when that runs out it is likely those planes cannot fly. They can cannibalize parts from other planes but that means fewer planes left able to fly. In time, there will be none that can fly.
As for training, in the US I think fighter pilot training takes 18 months. And it is expensive. Whether other air forces do as well I do not know.
I can easily imagine the cost of training a pilot to be nearly as high as the cost of the plane.
What’s happening with the Polish (and/or other countries’) MiG-29s that were going to be transferred to Ukraine? Are they sitting in Poland awaiting disposition? Or are they being dismantled for parts for Ukrainian MiGs?
Around 1/10 the cost of the plane.
Still high.
Suppose a band of renegade Ukrainian pilots sneaked in and stole the aircraft, while the guards were out at a big party?
Only if they do a bad job. Otherwise I think they reuse the planes for other piliots.

Why NO ONE is Giving Fighter Jets to Ukraine
Stranger

Suppose a band of renegade Ukrainian pilots sneaked in and stole the aircraft, while the guards were out at a big party?
Seriously, though… The video mentions the sending of spare parts. It says that complete aircraft are just parts that haven’t been disassembled. What if the aircraft (once, as the video points out, they are downgraded) are disassembled for ground transport and delivered as spare parts – spare parts not seeming to rile up Putin too much – and the Ukrainians use the ‘spare parts’ to ‘make complete aircraft’?
(When I worked at Magic Mountain, I used to get patty melts cheaper by buying the components separately and assembling them myself. Unfortunately, they eventually caught on.)

Suppose a band of renegade Ukrainian pilots sneaked in and stole the aircraft, while the guards were out at a big party?
I’d make a movie about it titled “Stripes 2: Yellow & Blue” with Paul Rudd as a plucky Air Force captain secretly organizing the “unauthorized transfer” and Bill Murray in a cameo appearance as the US President who starts telling a shaggy dog story about the time he was in the Army and stole a disguised urban assault vehicle and invaded Czechoslovakia before his wife (played by Susan Sarandon) tells him to shut up because nobody wants to hear that ridiculous anecdote yet again.
Stranger
One, I’d watch that movie.
Two, why don’t we have a like button again?
It’s already been done: U.S. to send MiG-29 aircraft to Ukraine, but as a source of spare parts.
The Biden administration has reportedly sold old ex-Moldovan MiG-29 fighters to Kiev to serve as a source of spare parts to maintain it´s remaining aircraft.
According to different media reports, the MiG-29 fighters that Ukraine will receive are not in flying condition, and are part of a purchase made by the United States in 1997 from Moldova, for about twenty units.
US Defense Department spokesman John Kirby, without wanting to go into details about the type of aircraft supplied to Ukraine or their operational status, commented as follows; «They have more fighter aircraft at their disposal today than they did two weeks ago.» «Without going into details about what other countries are supplying, I would say they have received additional aircraft and spare parts to augment their fleet,» he then added.
That was from April 19th.

Suppose a band of renegade Ukrainian pilots sneaked in and stole the aircraft, while the guards were out at a big party?
I’ve thought of that, so it must be a ridiculously bad idea.
Call a couple of farmers with tractors.
Do you know what’s up with what I thought was the engine intakes on those airframes? They appear closed, though that’s maybe just a thing on the ground as they appear open in the air:
Also, aren’t they taking off pretty much from the grass at @2:00
They’re covered to prevent debris from being kicked up in there or birds and rodents from trying to nest inside the turbine. They removes those in preparation for staring up the aircraft. Despite what you see in Marvel movies, it is very, very bad to land or take off a jet aircraft in a dirt field or on a runway that has not been thoroughly de-FOD’d (foreign object debris).
Stranger
In the USSR all pilots inc the commercial pilots were military trained.
Yes, the planes they flew might have been short on maintenance and fuel but when you boarded an Aeroflot you knew the guy up the front could really fly a plane.

Despite what you see in Marvel movies, it is very, very bad to land or take off a jet aircraft in a dirt field or on a runway that has not been thoroughly de-FOD’d (foreign object debris).
When I was at EAFB, a B-1B was FOD-ed when a maintenance crew member left a socket wrench in an intake.
It is critical to shadowbox all tools used around aircraft and missiles [edit: ninja’d by @beowulff], and maintain a count on all fasteners and other potential FOD. There is a long history of catastrophic failures because of a misplaced tool or nut, and I’ve made that observation again and again during reviews in facilities where the discipline isn’t apparent. Oddly, this is something that many of the young commercial start-ups seem to be quite good about while it is the long-established contractors who get sloppy about it.
We once found a paperclip causing a short inside a sealed flight controller and when asked about how that could possibly happen on an avionics propulsion floor, a tech pointed to their work travelers which were all grouped together with paper clips like this was some kind of law office. I thought the senior avionics engineer on my team—a guy who was chill about nearly everything—was going to pop a blood vessel, and I and everyone else in the bay had to hear his recitation of every failure he knew of due to loose metallic fasteners, coins, jewelry, and bits of solder that had occurred in his forty years of experience.
Stranger