As you are finding within the "What is Qi" article, there are various types so discussing "Qi" can be difficult without using all of the proper terminology - and even then it can still be difficult.
The concept of Jing and Yuan Qi (they get mixed to some degree) is that there is some aspect of our qi which is present at birth and that is all we get. Strong initial deficiencies would lead to conditions such as mental retardation, strong learning disabilities, poor physical and/or mental development, etc. In theory, other than building the post-natal qi there is little you can do about this initial deficiency - it cannot be built up.
Now a strong initial level of Yuan Qi does not necessarily mean that you will have a healthier life or a longer life span, it just means that you will have more reserves to draw from over a longer period of time. Yuan Qi cannot be in an excessive state, in theory.
For an example, someone with strong yuan qi faces a bout of cancer and survives - the amount of yuan qi that their body had to pull from to get through this period of illness was small in relation to the total amount so their overall lifespan may not be affected much. Someone who starts with very low yuan qi and experiences a stomach virus that takes a month to clear up may have greatly lowered their lifespan.
Now to continue the example, the person with low yuan qi decides to practice Tai Chi everyday for the rest of their life strongly building their post-natal qi and rarely utilizing their pre-natal qi - they may offset any changes to their lifespan through healthy living. And the cancer survivor decides to travel the world and go out drinking and dancing every night getting little sleep and strongly using their pre-natal qi to survive may use up their pre-natal blessings and pass on early.
The way I usually explain this go as follows: You are born with a fixed amount of yuan qi. The yuan qi is a catalyst for all of the functions in your body. The vast majority of these functions can run on any qi if it is available, but some require only yuan qi and if you have low energy then your body will pull from the limited resource of yuan qi. When the yuan qi is used up there is no more catalyst, so you die. Life preservation, then, is about maintaining usable amounts of post-natal qi in your body so your "need" to dip into your fixed amount of yuan qi is minimized.
The concept of strength, then, does not apply directly to yuan qi in the sense that you can build this aspect up - what you really want is preservation.
To answer your other questions, you would have to define "strength". This term can mean any number of things. Certainly you want adequate amounts of qi and to preserve them as well as you can. So building them with proper diet, exercise, acupuncture, etc. and preserving them with moderate lifestyle habits, staying healthy, etc. should be the focus. Having strong or plentiful qi is in and of itself not a problem. But how you build, or strengthen, this qi can be. And there are downsides to physical strength within Chinese Medical terms as well.
What it really comes down to is that you cannot just take tonifying substances and expect to live longer - if it was that easy we would find life increased by simply taking ginseng everyday. Your body has to be able to assimilate your qi into a usable format and store it when necessary. You could, for example, take tonifying herbs everyday but have excessive amounts of sex and physical activity and never build a surplus leaving yourself open for deficiency issues. On the other hand you can have adequate amounts of qi, and lead an immobile lifestyle and develop serious health problems and low energy due to poor circulation, physically and energetically. Also physical muscular strength constricts circulation so generally does not lead to longer lifespans per se.
Consider Yuan Qi as a fixed entity where the level of which in and of itself doesn't mean anything to your health other than you probably have more possibilities of not being greatly harmed by long term illnesses, periods of sustained stress, all of the things that weaken our post-natal qi and require us to tap into our resources.