The Russians stated the terms for the Special Military Operation right when it started. The Russian President stated their objectives. Denazification and neutralization. The Russians won't accept a non-neutral Ukraine.
Like I said before, you could expect a similar situation to what happened to Finland in WW2. Russian troops would be indefinitively stationed inside Ukraine to guarantee their neutrality and Ukraine would need to get rid of all their heavy weapons. Armor, rocket artillery, etc.
As for how much territory Russia will take over the next years, it depends really. Russia already decided it needs a security cordon to guarantee the safety of its own territory, they will push the Ukrainians back to establish this. If it will be enough to be outside conventional artillery range, HIMARS range, or Storm Shadow range, it depends on the availability of those weapons and their use by Ukraine.