DND Online
Class / HP
With respect to Character Creation, when determining abilities, roll 4d6, drop the lowest die roll, and select the order you wish to proceed with (D&D Beyond). Your character should also start at level 1, with 9-16 more HP than normal. Note that there are no Artificers at this time.
House Rules
House Rule #1: Whenever your character drops to 0hp, you become unconscious. Note that when your character drops to -10hp, he or she dies. Note: that all rules are open to discussion before a final decision is made.
House Rule #2: Undead heal from Necrotic damage, and unless killed by critical or radiant damage, it rolls a d20 to determine if it proceeds further; 10 and above: it keeps going.
D&D Beyond
Your backstory should be based on the provided storyline (initial railroad). It is what proceeds the main storyline that is sandbox based. You will start character creation before you reach this point. During Session 0, you will have a chance to talk to the other players about how everyone is proceeding after the initial one-shot. (See the Session 0 PDF.)
With respect to building your character with D&D Beyond, I would recommend WASD20's 5E Character Creation video. There are other videos on YouTube as well that cover character creation like SuperQuintastic's video. if all else fails, feel free to contact me. I will get back to you as soon as I can.
One-Shot
Session 0 is expected to last 2 hours. Session 0.5 should be at least 1 hour. During Session 0.5, players will have a chance to put their characters to the test. All decisions re: race, class and equipment must be made prior to Session 1. For those not familiar with Foundry VTT, check out Encounter Library's Foundry VTT video. There is also a shoter video by Cantrips Media.
Character Finalization:Characters need to be finalized before Session 1. This info supersedes all prior references found elsewhere. All sessions are two weeks apart. Use Discord where necessary (or contact me directly). With regard to character creation, I am quite flexible; Session 0 is an important start to any changes. (Feel free to request a game discussion for anything related to the game. If three of you request one on Discord, we will lengthen the session by 20 minutes.)