The DOS era of gaming covers a wide range from early 80s to late 90s. Rather than trying to build a "DOS" PC per se, I would think more in terms of respective eras of gaming you want to cover. You specifically mention Maniac Mansion (1987) and mid-90s (Quake, TekWar). Depending on which games you want to play, will dictate the type of build and video/sound options you will need.
Given the wide range of DOS gaming eras, I also wouldn't ignore a Windows 98 build as an option for DOS games. My own 'Ultimate' Win98 setup (Athlon 2000+, GeForce Ti 4200, Diamond MX300+MIDI wavetable), can run late 90s Win 9X games, but is also perfectly suited for early 90s DOS gaming like Doom.
Prebuilt versus scratch builds
Prebuilt systems are nice because you are getting something that is tested and works. I've bought several prebuilt retro systems for this reason. They are more expensive, but not having to deal with hardware troubleshooting can be a blessing. Plus, they are can always be modified based on your own goals.
Scratch builds can be fun but it can take longer to collect all the necessary parts and involve more troubleshooting and refurbishing. Though the latter is a good learning experience in keeping retro hardware working.
Sound Options and DOS games
Given the wide era of DOS gaming, sound options can get complicated. To simplify, I tend break down audio options by era:
- early 80s - PC speaker
- mid 80s - PC speaker / Tandy 3 channel sound
- late 80s to early 90s - Adlib / Sound Blaster / Roland MT-32
- early to mid 90s - Sound Blaster Pro (& compatibles) / Roland MT-32
- mid 90s - Sound Blaster 16 (& compatibles) / Sound Blaster AWE32 / Gravis Ultrasound / General MIDI (Roland Sound Canvas, etc.)
- late 90s -various PCI sound cards
This list is nowhere near exhaustive, since there are a *lot* of DOS sound cards and sounds options (MIDI modules, wavetables).
Do you have any specific goals for sound support? Are you looking for the best possible audio from the respective eras of DOS gaming? Are you looking for broad compatibility? Are you looking for a specific "sound" from that era (e.g. FM synthesis like OPL2/OPL3 versus MIDI devices like MT-32).
If you have some initial goals, that can help narrow down your choices.
When dealing with retro hardware, hardware failures comes with the territory. Learning basics electronic troubleshooting and soldering skills are invaluable when it comes to maintaining old hardware.
Retro PC-building is enjoyable and rewarding. Don't worry about getting everything "right" the first time. Part of the fun is the journey, exploring different hardware options and ultimately working towards systems that meet your personal goals.
Have fun with it! 😁