To expand on my previous comment over a decade ago, no need to choose. Get a pool table with a dining table top. There are loads available. Then cut yourself a piece of MDF or decent quality plywood to fit on top. Make the dimensions enough to allow for fitting a net. EITHER paint it in your own colour scheme as a ping pong table - maybe to match your choice of pool table cloth. Doesn't have to be green & white. Mine's blue & yellow, to match the funky bats & balls I found. OR make the top side a piece of art. hang it on the wall when not in use. You can play ping pong on any sized table. Mine's about 1m x 2m as that's what I can easily store. (Sadly no space for a pool table, but we do have a wide bodied pinball machine & our local pool club, with three pool & two snooker tables, is a 5 min walk away.) You CAN have your cake & eat it.

With pools and modern houses, I think bold simple schemes work well. Ornamental grasses planted en masse would look effective. We surrounded a pool with Miscanthus sinensis interplanted with Verbena bonariensis in thin beds for one job. However, given the size of your planting area, this might be too large an area for this treatment. My other suggestion would be to go for a sort of Mediterranean scheme using blocks of small shrubs such as Cistus, Lavender, Hebe, Rosemary and Euphorbia wulfenii. These could be planted in drifts to a selected colour palette and then infilled with grasses and drought loving herbaceous like sedums, salvias and agapanthus. The shrubs work well in that their evergreen foliage and twiggy nature trap the leaves and prevent too much debris blowing into the pool.

@fizzfan54 - Yes, not everyone can afford them or would even have space for them. My own balcony would be a tad squeezed if I added one (not to mention that it might annoy the neighbour below), but as a dream feature, it's fun to toy with the idea!

forzaitalia is right , you need a specialist or two to answer your questions. Something to think about though, if you have a clear 20metre run by what will probably need to be 7metres wide,that is a huge space, if not and walls need to come out, then there will be some serious structural work to be done. The size you are considering will hold about 120 - 150 tons of water so the foundation and construction of the pool will need to be enough to support that, also depending on the area in which you live you may need a ground survey for any services that may be impacted by the work, you will need a survey of the property and foundation anyway to assess any impact such a construction may have on the property. A professional pool constructor should be able to answer all of those questions and probably some I haven't thought of.