Should I buy the DM Guide and Players Handbook?

I'm running Lost Mines at the moment using the official module, so all the creature stats etc are available. If I were to buy the DM Guide and Players Handbook, what advantages would these give me if I were only going to play paid for official modules, such as Horde Of The Dragon Queen, Out Of The Abyss etc? EDIT: Monster Manual as well... Also, if I buy the Players Handbook, are my friends able to gain access to all the extras when creating characters within games that I'm running? Or will they need to buy their own copy?

The player's handbook contains all the basic classes, subclasses and professions. You can put these in by hand but drag and drop from the compendium is way easier. If you buy the PHB, up to 5 friends of yours in 1 game will be able to share it. The DM guide is useless for roll20, I'm not even sure if it's available. ... well, the DM guide is useless anyway. rules are for players. The monster manual is way less useful than the PHB because it's situational. How often do your players encounter weird ass monsters? How often are those monsters homebrew anyway to fir your theme? The roll20 benefit is to look up the monster and drag it directly on the board. Even more situational, since many GMs prepare stuff like that beforehand. Adventures let you start immediately and put in less work on the minutiae of the adventure, but they're one-shot per group of people. They contain some nice maps, but that's it. The replay value is low. I think the most important question is: are you a DM? Do you plan being one?

Echoing Frankye here. If you are planning on primarily running modules, all of the statblocks and art from the official publication will be available. PHB will be very helpful in allowing your players a large range of character options. I would highly recommend it for this play style. After that Xanathars and Volos would be nice later additions to increase class and race options, but not nearly so much as the PHB. The Monster Manual would be of greatest use if you like to tinker a lot with the modules and add a lot of homebrew content. But you could do a lot of that manually, or through adapting the free monsters that come with the base compendium (the SRD). Purchase of this depends on your play style and may not be of much value to you if you cleave pretty closely to the published adventures. The DMG is not yet out, and honestly, aside from adding a few magic items and class race options that few people use, I'm not sure of how much use it will be, other than making the rest of the rule set available to Compendium lookup.

That's what I thought guys, cheers.