Which skills are best for each position is still guesswork for all of us if everyone is truly honest about it. Some seem pretty straightforward, while others are just a best estimate and everyone has their own opinion. If I recall correctly, the list you made was done a long time ago. Some may still go by this list. I agree with some if it, I disagree with some of it, and some of it I'm still not sure either way. And I think most people will be similar in their opinion towards this list. And there really isn't a way to tell who's right or wrong on any of it.

My best advice, is train fitness skills (speed/strength/stamina) first until speed and strength cap (do NOT train stamina to 20), then determine what position you want to use the player based on their speed and strength. Then train obvious relevant skills for that position and maybe a less obvious but plausible skill as well.
As you play and read the forums, you will develop your own opinion and read others that may influence and you can adjust your training based on that.

One thing I did years ago that helped me make my list of skills is to search games for players with 5* game ratings (on the stats tab) and scout those players to see what skills were trained high for those positions. It took a long time over several seasons to compile a large enough list to make comparisons that seemed useful. And still I'm not certain on the accuracy of my data.

As to your initial question, in my opinion, vision is important for LB's (especially MLB), but not important for TE's. Again. Just my opinion. Others will differ.

Still trying to determine that one myself. I do believe INT is needed for MLB. Based on how the game engine is suppose to work, I would think that it wouldn't necessarily be needed for OLB. However, most top end OLB's I've scouted had high INT and most of the time I use high INT OLB's myself. I currently have a couple of OLB's with lower INT I'm trying now so we'll see how they perform.

I'm getting to the point of getting buildings (having maxed out my VIP/Exec seats) and could do with a little guidance on coaches. Is there any thoughts on getting a level somewhere between 1 and 20, or am I right in thinking that if I'm investing in coaches of a certain "type" I ought to go straight to level 20?

I've got my fitness hall, so initially thinking of investing just in fitness coaches, until I build the training hall also (which I'm hoping won't be too many weeks away, now I'm getting good ticket money from home games)