for basement thing, you can split your terrain into 4 parts and leave a hole there.

also i am guessing 3 can be achieced with a custom shader?

These limitations(rectangular,cannot be rotated, all vertices has same space between them) are the point of the terrain engine, by having these limitations, it can make a lot of assumptions instead of calculations which makes things a lot faster. If these limitataions were to be removed, they would not be much different than models and that would not make any sense then.

1 and 2: I can´t think of a situation where this might be a problem? And if it is, you most probably don´t want to use terrain anyway.
3: Shaders are the way to go...
4: Be creative I could imagine a terrain with some transparent parts in it and some regions disabling collision with the terrain. Shouldn´t be very hard.

Edit: Some idea on the topic would be to use a big model moving with the player on a fixed grid based on the vertex distances with a higher vertex distribution at its center. One could then generate an heightmap on the fly based on the position and set the vertex heights within the vertex shader. The collision detection can be done manually with the heightmap image.

Lol I almost would take this as an insult. I am not a total n00b I just don't ask for help unless I have no choice (the whole I can figure it out on my own thing). I have been using 3DGS since A5 lol. Actually what I am trying to make is a very complex space flight sim with photo realistic graphics and motion simulator control (I have a purpose for this). So far it is actually coming along quite well, and I have to use A8 because of support for the netport IO module.

That being said, I appreciate everyone's help, the infinite terrain idea, although not what I am looking for, may do in a pinch if it must. Just been running into problems trying to get the terrain for such a large scale to look good

I have mastered the infinite terrain with high detail. It takes time and patience, but you could literally create terrain up to a few million quants wide. I just finished up a book and tutorial on it. It has taken me almost 3 years to problem solve this, but I finally have mastered it.