What's the difference between Solo and Online Multiplayer in Elite: Dangerous? If I have a Captain in Solo, will they continue if I play in Multiplayer, or will I start over?
What are the major differences and similarities between these two modes?
There aren't many differences. You use the same CMDR save file in both solo and open, the background simulation is the same, so the standing of minor factions will be consistent, the only difference is that there are other players in open play, and, obviously, there are none in solo.
Open play can be slightly more dangerous in that regard, since you can run into CMDRs with no regard for the law, and who will usually be more skilled than an NPC pirate.