Yes, it is generally okay to oversize a well pressure tank, and it will not harm your well system. The primary advantage is that a larger tank reduces frequent pump cycling, leading to longer, slower cycles with fewer startups. This can result in less wear and tear, potentially increasing the lifespan of the pump and conserving energy. However, there are drawbacks to consider. Oversized tanks have a higher upfront cost and require more physical space. While not necessarily a bad thing, opting for a tank that is appropriately sized for your well is often the most efficient choice in terms of cost and space.

While dry wells can be effective for managing rainwater, they have several disadvantages. They can become clogged with sediment, especially after large storms, which reduces their effectiveness and can be difficult to clean. Dry wells are also not suitable for all soil types; they will not function properly in soil with low permeability. Additionally, if a dry well is not large enough to handle the amount of rainfall in your area, it can overflow. For gravity-flow models, the water may disperse very slowly, depending on the well's depth and the soil's permeability.

Most deep wells can be expected to last somewhere between 30 and 50 years. This assumes that the well and all of its components are properly maintained on a regular basis. During this time, it is unlikely that modern deep wells will run dry over the course of their typical lifespan. That is one of the biggest benefits of digging a deeper well. 

The efficacy of a drain field depends on a wide variety of factors, though a well-maintained one can last as long as 40 or 50 years. Of the different types of septic tanks on the market, concrete and plastic tanks tend to last the longest—upwards of 40 years if they’re pumped regularly—while steel tanks have a tendency to rust over time and may need to be replaced after 15 or 20 years.