deepthaw

If you want the full DOS experience the best bet is a 486 otherwise you're better off with DOSBox. Pentium systems will run too fast for many older titles and like mentioned before you will need to slow them down (PITA to be honest). There is always the option of just running your CRT and mechanical keyboard on a later rig with DOSBox and that will give a close-to authentic experience.

It's a bit like arcades. Mine use 3:4 LCDs. Running Mame with scanlines. I've got everything I want on there, all the systems. Full arcade controls and coin mechs. But of course you lose the authenticity, though as above authenticity can be a complete pain in the arse. 🛠️ On the other hand, a lot of 'authenticity' is bollocks, I mean when I was a kid and in the arcades, all the machines were pretty beat up, the monitors were not the best the sticks/buttons were worn out and unresponsive sometimes the control panel was a bit sticky. 

DOSBox isn't recommended on a Pentium 4. You're going to run into performance problems with certain games and so you might as just use a modern machine if you go that route.

What I'd recommend is turning it into a Windows '98 machine. You will then have the ability to play many (not all) DOS titles, as well as quality Windows 95 and 98 releases from the era. Even some XP titles will still work on '98, depending. Regardless of what you do, you will have to figure out how things run from game to game. Some games won't load at all, some games will load but will run too fast, while others will be perfect. It's not a perfect setup, but it's at least flexible.

Sound Blaster Live cards have SB16 emulation and will work with DOS titles. There are other cards from other companies/manufacturers that will also emulate (or replicate) SB16 functionality in DOS titles.