If Ukraine wins this war, then there is absolutely nothing that will prevent Putin/Russia from rearming and attacking Ukraine again! What guarantees are there that Putin/Russia won't attack again? Only NATO-membership will be able to prevent that!
Hasn't history showed that Putin/Russia will be back?
If I had any say over Ukraine's military after a win for Ukraine in this war, then I would never, ever, ever agree to any kind of ".../ nominally decrease the size of its standing army /..."
Never in a million years!
I would up the fighter force with at least 50% compared to pre-war figures. And those fighters would ALL be F-16, F-18, Jas Gripen, Rafale, Eurofighter or F-35.
Patriot missiles or some equivalent.
Get attack helicopters or get something that can serve as a budget A-10.
Get a *sugar* ton of Bayraktar drones.
A *sugar* ton of Swithblade drones.
A *sugar* ton of Javelins and AT4s or some such.
Keep the number of tanks at the same level as before the war but replace existing ones with top of the line western stuff. And of course keep the existing replaced tanks in mothball storage.
Get some 3 diesel electric submarines.
A sufficient number of anti-ship missiles.
The Ukrainian leadership are no fools and understand Putin's long term goal,.
It was also Putin's aim to win in 3 days with minimal Russian losses and removal of the Ukrainian leadership, we know how that plan worked out.
Sanctions should be tightened as far as possible reduce the Russian economy to rubble, that is the best guarantee Russia will not be back,
At the end of the war the Russian army will not be in the same state it was at the start, soldiers returning home will also allow news of the real nature of the war to leak slowly out.
It may take a decade, perhaps longer, to rebuild the Russian army back to the sate it was in at the start of the war, in that decade the West move away form Russian oil and gas.
Ukraine doesn't need a large standing army, a lot of the populace have military expiernece of actual; combat in this war and a lot more have some training.
A small rotational army with 1-2 years of training should be sufficient.
I also think a security guarantee from Turkey is very significant and would give me a lot of comfort if I was a Ukrainian.
A security security guarantee from Turkey alone should be enough to make Russia think twice and it would be very unwise for Russia tor test this,
Finally do a good job of levelling the Russian economy and moving away form oil and gas, it isn't coming back soon, in 10 years time the Russians will realise they have spent the last 20 years going backs in economic terms.
Sanctions on/off isn't a binary switch, there is a lot of murky detail and shades of grey.
As well as imagining a quick military victory, the Russians are imagining the economy will bounce back quickly after the war, and life will return to normal, they are delusional on both fronts.
Putin and a lot of his support base are an older demographic and generally not in good health for their age group. Many of them may die off even before Russia has rebuilt the army, and certainly well before Russia has rebuilt the economy.
The time to give Russia economic assistance is when we see a change of attitude from their leadership and all necessary Russians handed over for war crime trails. If that means 20-30 years of economic hardship for Russia, that is what they deserve.
People might say China will prop up and bail out Russia, But apart form cheap food and Fossil Fuels Russia has very little to offer, the Chinese will soon find money spent in Russia doesn't achieve a high ROI.