Current gen SSD vs 4 year old SSD questions

I have a Corsair Force LX 256GB SSD which I now use for OS, system apps and main games. It was the only drive in my computer up until 6 months ago and has had moderate use over the past 4 years. It has been formatted 4 times that I can remember. I have a few questions about it and a possible upgrade.



What sort of lifespan can I expect from it? I understand that there is a limited number of writes that can be performed before it dies.



I see articles about how much faster new SSDs are. Is this only for specific use case scenarios like massive files being transferred and say, content creation?



How much has current gen SSD tech improvements improved gaming load times over my older drive? How much faster will a new Evo 960 be for gaming, if at all?



My motherboard only supports PCIe M.2 cards so a more expensive NVME is necessary rather than a SATA M.2, would I be better off with a 2.5" Evo rather than a M.2? Are there any trade offs?



As I understand it, not having an OS on drive will improve load performance in games.



I need more space as the 1TB HD I bought 6 months ago is nearly full already, so it's not a case of should I buy, but what should I buy. Yes I know that a SSD will be vastly superior speed wise, and a HD will be more storage per dollar. I'm looking at SSDs now and already have an idea what to get to increase bulk storage.



Thanks guys.