Tooth veneers are for life and composite resin to fill in the top teeth triangular space, as gums recedes, maintains more of the natural teeth?

Wrong way around. Gum recession needs attention first. See periodontist to halt recession. Then work w your dentist or a prosthodontist to reshape and re contour teeth. Know that "permanent" restorations have a finite life span and need periodic maintenance.
The term for life is. Misleading. Nothing is for life. Everything has a finite life. Some people put for life in bold to entice people and then in microscopic print have "of the appliance or device or whatever". Everything will need replacement at some point in time. The when depends on you - hygiene, diet, habits, clenching or grinding, dry mouth, smoker, alcohol and the list goes on. Hope this helps.
'Black Triangles' As they are called can be a cosmetic problem. How to treat them, if at all, is a subject too lengthy ; complex to discuss on this site. Having said that, composites are usually more conservative but may be more difficult to properly contour. Periodontal health is also a major concern (either way). Find the best periodontist ; restorative dentist you can for a consult. Don't focus on 1 factor alone.
Contours. The contours, shape of your veneers and/or resin-composites have to be developed precisely-- if overcontoured or overhang, not good at all for your gums, --inflammation and other issues, also need to consider durability when flossing, proximal contact, biologic width--needs to be a natural emergence and blended in naturally. Note, nothing lasts forever, important good homecare and hygiene, too!
Veneers. Nothing is for life- the longest lasting thing in dentistry is actually gold, but most people don't want it on their front teeth. Veneers when done well can last a long time. Composites need to be shaped well and follow the lines of each tooth. If they are too bulky they could be a food trap.