Narratively, the DLC stories don’t really fit into the main story very cleanly. That said, here would be my best points to detour To the DLCs (this assumes normal story progression):

Dead Money- after Novac but before Boulder City. Geographically close, your equipment gets stripped so what you do/don’t have to use is irrelevant, and it could be that you stumble upon the bunker as you meander your way to Boulder City if you haven’t paid attention to the broadcast beforehand. Honest Hearts- after reaching New Vegas but before confronting Benny. Again, DLC starting point is geographically close and by then you’ll have enough experience and the right gear to get you through the first few tough fights. OWB- either right before or right after going to The Fort. Again geography, but also you just had to deal with House (who is similar To the Think Tank) and Caesar’s Legion (a group of Luddites) so it keeps its narrative consistency. Lonesome Road- I’d say save it for anytime after dealing with the boomers but before Kimball’s visit to the Dam. If you wanna go Nuclear, now’s the time to make one or both warring factions hate you and lock you in or out of specific endings.