You've selected DDR RAM when your motherboard takes SDR RAM. This is a little harder to find and a little more expensive. 256MB will be plenty for Windows 98 games and if you keep it to one stick that limits your chances of errors.
The Compaq board may have proprietary front panel headers, so make sure the case has individual pins for the various buttons and LEDs.
If the PSU goes it will be hard to track down another. If you had a retail 370 board then you could use any modern power supply for this build but the board would be a lot more expensive. It does seem to be quite weak but it's the sort of system it would have powered originally...
The graphics card will be fine and is a sensible cheap option. It may struggle to run later games (2001) at max settings and high resolutions and frame rates, especially if it had a 64bit memory bus not 128bit.
What is the model number for the Live? Some OEM ones need specific drivers, people have the most success with 0060 and 0100.
DOS support is... Interesting. Give it a try and see what you think, you may decide an ISA system will be needed.
The board will probably not support tualitin CPUs so you're limited to 1000MHz ish. Given the (sensible) budget nature of the PC this in practice may be more like 800MHz. Perfectly functional for Windows 98 gaming.
Once the RAM is swapped it seems like a sensible first Windows 98 PC. It will play games (well) to 2001 or so