Midnight inspired campaign

[Quietus_One]

Hello, Aspiring midnight GM here. I've recently got hands and read a lot of the first edition sourcebooks, and I'm feeling pretty inspired to create my world and campaign based on that. It won't be a one-to-one correlation though.

The differences -
1) I run mostly in 5e or True20, so I'll be converting the monsters, NPCs. Maybe add in a few different ones. Nothing that breaks the lore.
2) Maybe a slight change of tone, less grim and more noble.
3) Ending it on a epic note - ending the threat of Izrador.     

What remains the same -
1) All the lore, as far as I can manage. 

What I want, and what I've got -
First of all, I want to give the players the whole tour. They hit all the major locations - Sarcosan, Caraheen, Baden's Bluff?, Dwarfholds, Erenland, and Theros Obsidia (and more, if it is somehow possible). I know I'm going to begin in Sarcosa, and end with Theros Obsidia - it's the middle that's the problem, since I don't want to back track. I do want to hit the players with the hopelessness at the beginning, but as they get stronger, I do want them to make a difference. No ifs, buts and maybes.

How you would go about this?

[Luiniel Blades]

The Crown of Shadow Sourcebook has a continent spanning which does a pretty good job of showing off the world.

The campaign starts off in the Western Kaladruns in a Surface Dwarf Holdfast of Durgis Rock. From there, it has the players go southward briefly and meet a wandering, diminished clan of Dornish refugees. Then down into the mountains where they can run into an underground Clan Dwarves holdfast. After that it moves them west along the Sarcosan plains where they meet some Sarcosan Freeriders. After that it hits the central river where the PC's meet gnomes and head North until they reach the Pellurian sea where they ride with some pirates heading Westward again to go to Baden's Bluff, which is the big central city that is still operating but is under moderate to heavy Shadow occupation. Then they head west again, traveling past the Burning Line where they see the war effort against the elves. Finally, they make it to the central elven forest of Erethor where they meet the Witch Queen Aradil and that's where that campaign ends, officially.

It offers a lot of setup and potential future plot hooks along the way. It lets the PC's get a handful of levels along the way to get stronger and gives the them a chance to see the world and how bad things have become. Also, it offers a few chances to do some real good along the way.

There's a lot I didn't mention, but one of the big things in the beginning to help set the tone, is that your PC's meet some truly incredible people. Levels 10-12, and they end up dying in the second big encounter. So if you're looking for some initial feelings of helplessness, that's a pretty good way to go about it.

[Chaotix]

Depending on how quickly you're planning to run this game, you might consider waiting for the 5e conversion officially underway and slated for release next year. That would be significantly less work than doing the conversion yourself.

If you're looking to run sooner though, then I agree Crown of Shadows is the way to go. Though, if I recall, it doesn't give you any tour of the Northlands, nor does it take you to Theros Obsidia - so you'll have to expand on the campaign from where it ends in the Caraheen. There'd be no backtracking though if you go up through the Veradeen, into the Northlands, and down to Theros Obsidia. That'd be a solid run through of much of the continent.