1. Valve created few example maps like "Example UI", you can open this map and watching how UI works etc.
One day valve deleted supporting some function in code,it was few mounth ago, many people who using this code from Example UI from Valve get error, becouse of new update. Veryfunny part that they steal don't fix this error in Example UI (this tutorial map steal broken) some people like me have looked for fixing this. They don't care if someone don't work from Tutirial maps.
2. Only Valve decide to provide dedicated servers or not (for custom mods), few custom maps where on top 1 of all maps with half million subscribers and more then 16k online, they havn't dedicated server, as example - name of mod Realm of Chaos.
3. There are so many things that must be improved or fixed, but a year has passed and no changes. You can register on valve's dev site, create topic with solution but chance that someone hear you less then 1%.
4.You can't create new hero, only ovveride old. You can't create new model for hero so simple like in other editors, there are big guide for that.
You can't change regeneration, stat bonus (hp or mp) from attributes (streanght, agility ...) You must use all known system, or create alot of modifiers for every hero, item and events for hero that changes basic bonuses from attributes usingmodifiers.
5.In fact, promote your mod is very difficult, custom games system has a monopoly, especially from the Chinese side (there are the biggest team of dota 2 developers from CHN more then 10 peoples named Avalon Studio) they have very big support from asia, every created mod from them after 1 day in top 10 maps). Get ready for the audience of Dota 2, they can play in bad created mods with no logic, and then can hate realy cool mods created for 1 year.
Also, for several years formed a strong community of english speaking moders, they support each other too.
The main thing you need to know is that all the basic features limited so long to create something other then dota (new shop, more then 6 spells on basic UI, more then 6 items, custom hero with3d modeletc. )
nice
some maps on DOTA2 are using Blizzard Copyright and should be deleted.