For Speaker placement, I subscribe to sitting further away than the distance between Speakers. I'm in a small room with my setup, Speakers are about 6' apart (on center) and I sit about 7.5' away. I know my speakers are closer together than I would prefer, but that can't be helped in my room... It's just what I've got to work with.
What you've described seems to give you some good room to play with. Screen aside, I would target somewhere between 8' and 12' distance between your mains, depending on what you can fit. 8.5-9' apart, with your LP being 10' away should be pretty good.
I don't worry too much about the angles of the triangle, which I'm guessing is your reference to "30º angle for L and R." I find a little more benefit in my setup from a bit of asymmetry, so 1 Speaker is pulled a little forward of the other. They are pretty close to centered in the room, L-R, but the toe in angle is also slightly skewed. (In the end, I fixed a serious suckout in my FR by doing this, as opposed to keeping them perfectly symmetrical. It only took about an inch closer to me on the L, and changing the toe-in by 1/2" roughly.)
Anyway, depending on your gear and depth of the rabbit hole you want to jump down, you can always play with Room EQ Wizard to take measurements, or Audyssey will show you the raw graph if you have the XT32 App... Dirac is good for seeing the measurement too, I think. Regardless, I was able to fix the worst problem in my room just by tinkering with position.
Going back to your question about distance... this will mainly affect how loud your Speakers are at your LP. For every doubling of distance, you will lose 6dB (outdoors). If your Speaker is rated at 90dB @1m, then 2m will be -6dB, and 4m will be -12dB. Inside, you get help with boundary support to a certain extent and may only drop -3dB at each doubling of distance.
This really only matters if you are trying to get full-on reference level playback at THX levels, say. That would by 85-105dB at your LP, which is pretty loud by most peoples standards.
A rough example would be having Speaker A with an 86dB sensitivity and Speaker B with a 92dB sensitivity.
Speaker A will hit 110 dB with 256w @1m. Speaker B will hit 116dB with 256w. Subtract for the distance from, and you can see the effect. Speaker A, if it can handle 512w, would get to 113dB at 1m, which could be enough to fry some gear.
But if you are listening to that Speaker in a large enough room, and you are far enough away, it will not hit reference level.
Dunno if that answers your question very well.
It is complicated by many variables, as you can see.
If it were my space, I'd be happy sitting about 10' back with a spacing of 8.5-9' (as I gave the example earlier). I'd be happy having ~3' from the front of the Speaker to the front wall, and having plenty of room behind me still for proper placement of my Rears.
In general, it seems that's pretty close to what you have right now.
How far apart are your Mains?