Installing carpet over carpet may affect the warranty of the new carpet. Check with the manufacturer or retailer regarding their warranty policies. Many warranties stipulate specific installation guidelines, and installing carpet over carpet may not comply with these requirements. Voiding the warranty due to improper installation methods can leave you without help in case of issues or defects with the new carpet.

A 65-oz. carpet is good, and in many cases, it indicates a premium carpet. Most carpets for homes should fall in the range of 40 to 60 ounces for face weight. If a carpet has a 65-oz. face weight, it is likely more durable and long-lasting than a similar carpet with a lower face weight. Carpet face weight is just one factor in determining a carpet’s quality. 

Yes, carpeted stairs are generally considered safer than stairs with hard surfaces like wood, vinyl, or tile. Carpet provides more traction, which helps reduce the chances of slips and falls, and its cushioning can lessen the severity of an injury if a fall does occur. Hard surfaces often lack the friction needed for a secure tread and can be quite slippery.

However, it's worth noting that some carpets can also be slick, particularly if they are brand new, dirty, or made from certain materials. If any stair surface feels too slippery, traction treads can be added to most materials to increase grip and improve safety.

While it is possible to install carpet yourself, it is a challenging DIY project that requires precise measurement, proper cutting skills, and knowledge of correct installation techniques. The process involves multiple steps, including removing old flooring, installing underlayment and tack strips, and stretching the carpet to prevent wrinkles, which can take several days to complete.

Before starting, consider these factors:

• Warranty: Many manufacturers' warranties are voided if the carpet is not installed by a professional.

• Tools: You will need to buy or rent specialized equipment like a knee kicker, carpet stretcher, and seam roller.

• Complexity: DIY installation is most suitable for simple, straightforward rooms. Projects involving stairs or floor vents are significantly more difficult.

• Cost: While you can save on labor, the cost of tools plus the risk of expensive mistakes—which may require re-installation—can make hiring a professional more cost-effective in the long run.

Given the potential for errors, voided warranties, and the need for special tools, hiring a local carpet installer is often recommended to ensure the job is done correctly and safely.