Is it still lucrative to "mine" Sia by providing disk space? How much will I need in order to make good revenues?
Offering your disk space is called "hosting" or "farming" (In opposition to "mining"). You set up your own pricing, but you have to be competitive in order to get file contracts. Top hosts target to $1-2/Tb/month.
If have access to cheap HDDs, under certain scales and setups you could make ROI in less than a year. Right now the network is still underused, but the usage is growing fast, so probably in half year or 1 year good hosts will be able to host dozens of Terabytes an be profitable. Of course you'll still need cheap hardware (24/7 server-like infrastructure) and good bandwidth. But the advantages, compared to mining, is that electricity costs are minimal and there is not a increase in difficulty over time: if you remain competitive, you keep getting contracts
Do you leave your computer on all the time? What about the cost of electricity? What happens if your hard drive crashes and you lose their files? Do you lose the tokens from your collateral? I have a junk pc set up that I don't use, perhaps I should use it for this.