Running BECMI and 1e modules set in Mystara/Know World. Started with the adventure in the Red Box Basic DMG as a small starter. Next was N1. Realized it was too deadly for level 1 characters and dropped a plot hook after the PCs explored the village to send them to U1. U1 is a great two-parter and the PCs love that they have a SHIP!
Backtracked and finished most of N1. It's very deadly for a 4 PC party of level 2 (at first) and level 3 (the final dungeon). The Paladin blew through multiple spell slots smashing the BBEG who dropped him from maximum to zero HP in one hit (and did the same to the fighter). The Paladin failed three death saves as no one bandaged him because the remaining 2 PCs and the NPC couldn't spare an action. He actually wasn't upset that he died as he got to be heroic! We currently have 1 dead PC, one unconscious, one at 6 HP and one at 5 HP. It will be very tense getting out and avoiding anything still left inside as we stopped the session just after the BBEG went down. I was so wrapped up in the nuts and bolts of the final encounter and describing it as vividly as possible I didn't realize how much the PCs loved it until the battle was over.
One session in town for N1, two to finish U1 and let the tension build as the PCs had to make a real choice between the plot hook I added for U1 (cousin has gone missing!) and saving a charmed town in N1. How much worse would things be when they returned? Three more to finally complete N1 and then a race to find a Cleric high enough level to cast Raise Dead.
The campaign is set in the default Mystara country of Karameikos. They started in the default town of Threshold where one of the PCs is from. N1 is set in Irenke a bit to the east. U1 was set on the coast in Sulescu so we had The Sinister Secret of Sulescu where the pirate captain had a log from the Isle of Dread amongst his belongings.
Next adventure will likely be B10 and you can see many others praise it highly so I'm excited to run it. After than will probably be X1. I mean, the PCs have a ship and a log as a plot hook! Then the PCs at level 5 get teleported to do X2 and I'll toss some Wrath of the Immortals stuff in there. The PCs might be interested enough at that point to do X4 and X5. I might at I4 Pharaoh to the mix if it seems appropriate. At that point... depends on the PCs.
I've divided treasure by 5 or more and converted many of the gems to gold. I see one other person divided it by 10. Most magic items were removed. The PCs have lots of money as U1 is a huge haul even at 1/5. There were two magic items from U1 - a suit of plate +1 I converted to mithril chain. I use variant encumbrance so saving even 20 pounds is nice. I also left in the cursed magic item as it will provide a nice "trick" for the PCs to overcome without it being too terrible. The only magic item from N1 was with the BBEG. There are 5 permanent items there and the players randomly chose a number from 1 to 5 as I couldn't decide what to have as loot. They chose 1 which happened to be a Bag of Holding so now the PCs have two encumbrance items. They also bought a cart and a mule. I think that tracking encumbrance was the right thing as it gave the PCs a chance of feeling more powerful when they could overcome problems but it doesn't obviously boost their combat power. Good thing they have a cart, too, as they'll need it to transport their dead friend in time to get a Raise Dead!
Converting wasn't too bad. Some monsters were straight conversions. Large parties seemed to necessitate a few extra minions for fights with a boss (either a large boss or small boss) in order to allow the boss to actually seem more deadly. Both N1 and U1 have a lot of humans that are straight PC class monsters, which was easy to do for 1e. Many, but not all, were straight converted to a 5e PC class. Some, like the captain of the ship in U1, were converted to a MM monster. In the module he's a 5th level fighter but I made him a Bandit Captain (seemed appropriate) in my conversion.
I did make a spread sheet with all of the converted stats in condensed form for that particular encounter as well as the new (and reduced) treasure. I never had to open the MM or do on-the-fly treasure conversions. U1 was reduced to 2 pieces of paper and N1 to 3. I paperclipped the pages to my fancy DM screen (a cut up card board box) and it was very valuable in clearing space and speeding play up.