The very best rules editor out there is the rules file itself. I sometimes use the one that comes with Fantastic Worlds, but it is so buggy and only messes everything up.
I sometimes lose the overview over what I am doing, especially when assigning techs and units. That is why I am going to prevent this for my next scenarios. For example, I write a list of Units, technologies and perhaps also city improvements.
In general, a list of units should look like this:
MACEDONIANS
1. Macedonian Phalanx
2. Peltasts
3. Prodromoi
4. Archers
5. Mercenaries
6. Pioneers
7. Maced. Cavalry
8. Thessalians
9. Light Infantry
10. Strategos
11. Alexander
12. Pezhetairs
13. Siege Tower
14. Catapult
15. Trireme
16. Transport
17. Hoplites
18. Hypaspists
19. Somatophylax (Guards)
20. Parmenion
PERSIANS
21. Bactrians
22. Cataphracts
23. Mounted Archers
24. Scythians
25. Chariots
26. Scythian Chariots
27. Greeks
28. Melophoroi
29. Persians
30. Pasti
31. Rshtika
32. Thanuviya
33. Ushabari
34. Elephants
35. Slinges
36. Garrison
37. General
38. Immortals
39. Ballista (Tyros)
40. Fortress
41. Phoenecian Galley
42. Cilician Galley
43. Memnon
SCYTHO-BACTRIANS
44. Scythians
45. Sacans
46. Massagets
47. Bessos
48. Spitamenes
49. Sogdians
50. Chorasmians
INDIANS
51. Elephants
52. Pikemen
53. Chariots
54. Chariot Archers
55. Infantry
56. Armored Chariots
57. Elephant Archers
58. Light Cavalry
59. Heavy Cavalry
60. Poros
--> 2 Unit Slots open for emergency!!!
(Yes, you guessed right - Alexander the Great
)
Then I try to write the techs beside them (which is why I usually do it on paper).
What I would advise you, however, would be the same thing I did when I first built a scenario having civ-specific units and techs.
I had it based on the Mediterranean map. It had 7 Civs, Persians, Egyptians, Athenians, Spartans, Etruscans, Carthaginians, but I can't remember which one was the 7th one (maybe Celts). I did it very simple. I viewed the instructions on editing the specific sections that is provided with the rules file. I also downloaded a file I found on "Ghost Technologies" (You can find a large number on instruction and hint files on editing the Rules.txt all over the net).
Then I built the scenario. I had the settlers build the units with all civs via cheat mode, did a little terrain work etc. etc. Then, I gave the Egyptians a special technology. I saved the game and opened the file rules.txt and named the tech "Egyptian Tech" and gave them a unit, "Egyptian Infantry". Prerequisite for this Unit was "Egyptian Tech". I changed the prerequisites for the "Egyptian Tech" No, No (Important!), saved the file, relaunched the scen - et voila! The Egyyptians had their very own Tech with their very own unit!
Something I would advise you is to build the cities before editing the rules file, because if your settlers need a specific tech (or they don't exist at all) it would be a bit complicated.
If you have any questions, write them here.