Right now buying a system isn't great as well ryzen refresh, rtx 300 and big navi are launching around the sepetmber window. With ryzen 400 coming in fall. A 5th gen i5 is going to just suck for every single thing you want to do with the system. So my advice is to either wait or see for a used ryzen system with a b450 or x470board is available.
New a ryzen 2700 + any msi b450 MAX board would be about 250 and that would just smash that poor i5 in your work tasks and be a lot better gaming cpu. This also will allow you to upgrade to a whole other 2 gens of cpu's in the future if there is need for performance (a msi tomahawk or mortar max are preferable).
Also the psu you are looking at is very low quality and should not be used as it is a risk to your system. Here is a psu tier list.Get a 500w or higher unit from the b tier or up.
If the stock is new or it was manufactured recently it will most likely support it
If it shipped with the old bios just ask a computer store to update it for you
Every b450 board that has a sticker that says "ryzen 3000 ready" then that means that it's guaranteed to ship with the new bios.
If you can wait
Save up more and wait for zen 3 and ampere and big Navi and if the prices were too expensive for you
You'll get last gen stuff got cheaper.