I've done two first level encounter tables: one for 4 PCs and one for 5 PCs. These are from the 5E Legacy SRD Bestiary. Import the code into a table using ; as the separator. These are smaller tables than I use since I normally use stuff out of the MM, MotM, and stuff from Kobold Press and MCDM. Note the two mismatched dice to roll the imported table will try to set a 1d15+1. The mid 5 will appear about 50% of the time and the two tails a little less than 2%. This mean humanoids are heavily favored to appear which makes sense in any dungeon that might have doors.
Any play testing of the tables would be nice. Those Flying Swords with that AC are likely to be problematic even with the number appearing having been that reduced. I'll try the tables in my next few "Let's Play" games. But replacing the Swords with Crawling Claws, Abyssal Wretches, Neogi Hatchlings, Slaad Tadpoles, Young Kruthik, Manes or Star Spawn Grue would improve the table, IMO. I usually use a larger table of 1d8 + 1d12, but I could not find enough dungeon monsters I would want to use vs. a first level party.
4 PCs:
5 PCs:Code:1d6+1d10 ; Group 1 ; Group 2
2 ; [1x] Acolyte ; [1d2+1x] Cultist
3 ; [1d2+1x] Stirge ;
4 ; [1d3+1x] Giant Lizard ;
5 ; [1d3+2x] Lemure ;
6 ; [1d3+1x] Skeleton ;
7 ; [1d2+2x] Kobold ;
8 ; [1d3+2x] Giant Rat ;
9 ; [1d3+2x] Cultist ;
10 ; [1d3+2x] Bandit ;
11 ; [1d3+1x] Goblin ;
12 ; [1d2+2x] Zombie ;
13 ; [1d3+2x] Giant Fire Beetle ;
14 ; [1d3+2x] Poisonous Snake ;
15 ; [2x] Guard ; [1d3x] Mastiff
16 ; [1x] Flying Sword ; [1d3+1x] Lemure
Edit: Updated the tables slightly changed the roll 2 from Acolyte & Commoner to Acolyte and Cultist. Reduced the Group 2 number (Cultist) appearing by 1. This was mostly just to increase overall table XP. I expect this to be balance neutral.Code:1d6+1d10 ; Group 1 ; Group 2
2 ; [2x] Acolyte ; [1d2+1x] Cultist
3 ; [1d3+1x] Stirge ;
4 ; [1d3+2x] Giant Lizard ;
5 ; [1d3+3x] Lemure ;
6 ; [1d3+2x] Skeleton ;
7 ; [1d3+2x] Kobold ;
8 ; [1d3+2x] Giant Rat ;
9 ; [1d3+3x] Cultist ;
10 ; [1d3+3x] Bandit ;
11 ; [1d3+2x] Goblin ;
12 ; [1d3+2x] Zombie ;
13 ; [1d3+3x] Giant Fire Beetle ;
14 ; [1d3+3x] Poisonous Snake ;
15 ; [2x] Guard ; [1d3+1x] Mastiff
16 ; [2x] Flying Sword ; [1d3+1x] Lemure
Second Edit: I released Let's Play: Side Quest! Building 5E Monster Encounters 2 which shows you how to copy the "Code" above into Fantasy Grounds and create an encounter table, and then generate an encounter you load into the combat tracker. Linking the video here with the code for anyone looking at this later.
Third Edit: Fixed creature name typos, changed: Bandits to Bandit and Giant Rats to Giant Rat. Note this is purely cosmetic at this time for 5E since that ruleset uses the creature name on the link which is singular.
Fourth Edit: Updated the tables for the latest (hopefully last) iteration. I changed the Flying (Diabolical) Sword to have Lemure flunkys, raised the min number of Cultist with the Acolyte(s) and increased the number of Giant Rats appearing.

