I had about 20k SPS owned, which is not nearly enough when playing in Diamond-Champion league, so I rent around 100- 300k more defending in my league and rating. The pros of renting SPS, of course, are to give you higher sps and glint multiplier, and you can also unstake your own sps without hurting your rewards. Cons is it may take some time for your SPS request to get filled, unless you pay for a higher price that will allow your request to be quickly filled.

If I remember correctly, 50k sps is enough for a bronze account to have x10 sps boost even when playing at silver rating. I do not know how much rewards you get on that, so I can't really say how it will work for you.