Firstly good luck. Though I've got no personal interest in a gay VN as a straight guy however as there are almost no such VN's to speak of there should be a gap in the market for you if you get a decent quality game out.
Ren'py isn't that bad, it's certainly easier than HTML ect. IMO, a little programming knowledge or at least knowledge of if/and/not/else ect. in programming is a boon, if you were to spend a few hours with a beginners python course (there are free ones around like code academy) you wouldn't even need to finish it to learn enough about code structure and programming logic to be able to make a no frills VN like acting lessons.
Iray is not such a simple answer, there are plenty of threads her on the F95zone that mention this, i'll list a few:
https://f95zone.to/forums/dev-tools-guides.44/ a good place to start for all things Daz
https://f95zone.to/threads/daz-studio-tutorials-tips.21586/ There are people who understand Iray and Daz, then there is
Xavster
https://f95zone.to/threads/how-to-optimise-render-times-in-iray-a-small-guide.24898/ recreation is great when it comes to assets in Daz, knows his way around a render too, pretty much should fit the bill for what you want
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Sickleyield is my go to when i need pro Daz tutorials and problem solving, she is literally amazing, great for getting more out of your renders and making complex little things work.
The main points are: more Cuda cores means faster renders, Cuda cores are Nvidia proprietary so you'll need an Nvidia GPU to start with, others simply won't cut it with Iray, they work much much slower, second you'll need Vram, the more the better until your running a little over the maximum you'll need, the rest is wasted, unlike Cuda cores which are not wasted.
Then it's CPu speed, again the more the merrier though it will have less effect than the aforementioned GPU specific specs, then Ram, though it has a lot less effect in renders than in scene manipulation(setting up to render)
There are ways to get more out of your hardware, using things like a scene optimiser lets you reduce scene size by compressing textures, so for example if you have an HD scene element that is too far away to get the full benefit of the HD quality you can compress the texture so it doesn't cripple your render time. Methods of lighting will effect render times as well, dim renders tend to take longer while brighter renders resolve somewhat more quickly in my experience so using good simple brightish lighting can both increase render quality and speed in some cases, ghost lights work well for this.
Additionally there are things like deleting things from a scene that aren't visible in the render to reduce the load on the hardware, going for lower render quality and higher resolutions then compressing down in PS as post work, in fact good post work in general will make up for quicker renders at slightly lower quality but that in itself takes time.
As for what i would want out of a gay VN, personal preference aside i expect i'd want similar things to want i'd want from a straight VN, a good story with a few unforeseen twists and turns along the way, don't let the story become "by the numbers" towards the end but don't make it needlessly over complex, Dreams of Desire's ending failed because of an overly simplistic and therefore expected ending for the most part, Acting Lessons on the other hand had a "bolt from the blue" needless complication in the form of a mad carrot (you had to be there).
Then there is pacing to consider, some VN's take forever to get going, Timestamps and A Wife and Mother are both culprits here, they either try to placate the reader with sex scenes with no context or just dump story early which is not engaging alone, sex isn't a replacement for story, story isn't a replacement for sex, you'll need a little of both in an adult VN and they should work together constructively, Depraved Awakening does this quite well, especially for a first time Dev's game.
Lastly and perhaps most importantly is cast, spend time making and writing your characters, cookie cutter characters are hella boring unless done exceedingly well. Keep your cast size small but not too small, develop them, have some contrast between them, have them interact with each other rather than just the MC and make then make sense as a character if the MC were absent from the game, characters shouldn't wait around for the MC's next action, they should be able to exist without his input, this is why a lot of choices based VN's fail for me, there is a feeling of the MC being in some way responsible for every little victory or failure, that the world revolves around him, good stories don't work like that.
Hope that helped a little and thanks for surviving to the bottom of that mound of text.
