I have a few questions

[Ch1r0n]

1. Can you mix and match games? I am personally a large fan in using 3.5 content and Pathfinder 1st ed content together. This helps mellow out some balancing issues of 3.5, and gives Pathfinder a bit more diversity. Is this a possibility in FGC, or do I have to use 3.5 in a 3.5 campaign and vice versa?

2. I currently have just about every 3.5 and Pathfinder book thats been released prior to 2015, are these sources usable or does someone playing have to have that particular module in the FGC system to use it. IE, can I use my PDF copy of Elder Evils to add Father Llymac into a campaign, or would I have to obtain the games copy of said book to use the content in Elder Evils?

3. Whats the max number of users you can have in a session?

4. How easy is it to implement house rules into the game. Like I have a house rule regarding matching AC. "If the attacker matches the AC of the defender, the Defender makes a reflex save (5+Ref save+dice roll) and if they beat the original attack roll, they aren't hit." Are house rules like this easy to implement, can you "program" the rule in like an automatic deal, or is it just like the real thing and the only thing the system handles is stat tracking and image for battle locations?

[LordEntrails]

Welcome!

1) Yes. PF1e is actually a child of 3.5 on FG and so you might be able to open both in the same PF campaign. If not you can use the Universal Module extension to allow you to open modules for any ruleset in any other ruleset. Just be sure to read the caveats in the extension thread. https://www.fantasygrounds.com/forums/showthread.php?41034-Universal-Module-Extension

2) You can use your own content/books/pdfs. You won't have the full FG experience (drag and drop), but you can manually enter any information you want. A similar discussion but for E is here; https://www.fantasygrounds.com/forums/showthread.php?32987-What-do-I-need-to-play-5e

3) 50? 100? There is not an imposed limited, but at some point the GM's network is going to make it impractical. A practical limit is probably in the 10-15 range.

4) Easy. Just adjust the results or add modifiers as you want. If you want automation, then it might take some more doing including writing an extension. It just all depends. You'll be able to answer this better for yourself once you start using FG.

[Kelrugem]

You can use all 3.5e and PF1 contents in PF1 and 3.5e campaigns, respectively :) No universal module extension needed for the modules :)