When should I release Ultima 2 Mod?

When it feels like a complete and cohesive product. Go through and make sure that every single thing in your mod serves a relevant purpose, or even has multiple uses. Tight-knit mods where everything works together in a well thought out way are far better than enormous mods filled with useless or one-time-use items.

Be sure all of your procedures work accurately every time, and don't expect the player to play your mod a certain way. Part of making a quality mod is by making its mechanics as robust as possible and suitable for all play-styles.

One of the most important things is how it looks- the textures. People like myself appreciate when the mod creator goes the extra mile in making consistent and good looking art. It can easily make or break the player's experience.

Don't rush anything. You don't have a deadline. People can wait. Polish is extremely important in everything people make.

Those are my values in making a mod and I hope you found them helpful. Good luck on your mod!

I agree with rmsandegs quality over productivity for sure.

As someone that has years of photo editing and texturing behind me as well as film and now learning audio I can offer some advice on some things to make your mod a bit better than I have found improves the quality.

Avoid making flat textures
It can be hard to make great 3D textures for items and blocks however the more time you put into the texture the better quality of them when you get better at texturing you can play with shading and shine effects. I am not sure what you are using to edit your textures but I personally use Paint.Net photo editor with the built bait plugin.

Research and Plan Beforehand
If you are making a real like gemstone look that gemstone up by typing the name of it in google search then select images. You can copy a real-life image and bring it into your editor then select the colors with any editors color picker to get the hue and sharing of that image. This can also be a good way to practice shading and shine effects as well.

Modeling and UV Mapping
This is advanced stuff but if you master it then you can end up making some sweet looking items and blocks. I suggest Cubik Studio because I know it culls things properly but if you don't have the money you can try BlockBench as it's free and supports entities as well.

Music and Sounds
This is more of an investment and will cost a tone of money and time to perfect but if you get some kind of studio-quality recording equipment then you can record sound effects in the real world for music there are paid programs like FL studio and much other software that will give you sound effects for your own royalty-free music that you can use for Dimension music and maybe even records one day.

Copying others work
If your making your own product may it be a mod, music or video always use your own work, this will save you from getting sued by someone that is PO for there hard work being ripped off, The MCreator community is a pretty good community with many people with good skills in specific areas, I am sure if you have for help for something like texture design you may be able to assemble a team for specific areas like modeling, audio and visual. It can take a long time to develop a mod and if you have people working in a dedicated area then you can speed up development and time from not needing to learn the skills. Just make sure to give them credit is some way when you publish.