Lincoln was a lawyer lawyer before becoming president. He handled some cases for railroads, yes. But they were not the major source of his practice. Not that that has anything to do with his positions to begin with.
And when Lincoln was inaugurated, seven states had seceded and had already seized all the federal forts, mints, and other facilities they could. They had two federal garrisons surrounded and at least one, Sumter, on the verge of being starved into surrender. The Confederacy were building their army and their intent was clear. There were no peaceful intent in any of that, and short of surrendering completely to every Confederate demand then there was nothing Lincoln could have done to perserve peace. Though he certainly tried.
I also think if Lincoln had lived, we would never have seen that shameful period in American history called Reconstruction. I do believe he was sincere about reuniting the nation while most Republicans saw the south as a conquered territory to be plundered and politically manipulated for own gain.
There is a lot of merit in that claim, but like everything else we'll never know. The Radical Republicans were very powerful and were out for vengeance. Regardless of how easy Lincoln might have wanted to be on the South they may well have had the numbers to force through most of their agenda.
Lincoln did quite well as a railroad lawyer. He managed to get his hands on some prime land as a result of his railroad work. I’m not saying he was any more or less scrupulous than any other railroad lawyer.
As for federal facilities, do you think the new United States would have acquiesced to the British maintaining military and government facilities in the US? They actually tried to do that to collect on debts owed to English citizens but in the end, the facilities were denied and the cases settled in court.
Lincoln was trying to negotiate peace. He was persuaded to break it off and use Fort Sumter to force a confrontation. To SC, this was a foreign fortress in the middle of their most important harbor. Sumter could have been evacuated but that was not put on the table.
I will agree we can’t know if Lincoln’s post-war policies would have been implemented despite Radical Republican opposition. I can only go by his stated intentions and give him the benefit of the doubt that he was being honest.
The victor always rewrites history to make his cause look just and the enemy deserving of every punishment inflicted. That applies to Reconstruction as well, which I blame for more racial animus than any other single cause.
The Radical Republicans did pass most of their Reconstruction program by overriding the Presidential veto of Andrew Johnson, so the numbers were indeed there. The real question is whether Lincoln could have convinced the Radicals to go along with his program rather than push their own. As you say, we will never know the answer to that.
I suspect that the real reason that the Radicals had the power that they did is that the prevailing sentiment in the population of the North was to punish the seceding states. I’m not a historian, so I could be wrong about that, but I don’t think you’d have so many Radical Republicans elected in the House without such a widespread sentiment.