What do you mean by "pure DOS"? Windows 98 SE installs its own version of DOS (7.1) and you should be able to select to boot into command-prompt only mode during startup. This is effectively "pure DOS" as no Windows drivers are loaded, to my knowledge. Knowing this to be the case, I don't see why it'd be necessary to boot here automatically, as it only saves a couple seconds at most.
Truthfully, I'm not familiar with this "DOS Starter Pack". I'll do some research on it so I can give you a more informed response. How familiar are you with DOS/Windows 9x? I typically avoid these kinds of repacks given my experience with working with these operating systems in the past. I've found it far more troublesome to try and work within someone else's parameters instead of just learning how the stock system works and tweaking it myself. Also, if all you're doing is stuff in DOS, shouldn't 6.22 suffice? The only reason why I wouldn't use it over the 7.1 included with 98 is because of the lack of FAT32 support, but 2 GBs is honestly more than enough for most people - trust me, DOS programs really don't take up a lot of space. You're gonna have more problems with memory management more than anything, as games tend to have specific needs as to whether or not they need stuff like EMM386, for instance, and memory management in general was a tremendous pain in the ass in DOS.
In any case, it should be very straightforward to just install 6.22 and go from there. I know stuff like driver setup and whatnot can be a pain, but I genuinely believe you'll be better off learning unmodified DOS 6.22 in the long run. Anyone can read the basic instructions a repack provides, as the person who created it has already gone through and figured out the hard stuff that goes over some peoples' heads. However, the best way you are going to fully learn how to troubleshoot common problems and work around them yourself is by starting from scratch and learning the quirks yourself. A repack, while convenient, forgoes this need to learn, and I find that can be very troubling in the long run. It will take a long time, but it will be worth it - I can assure you. I still have a tremendous amount of respect for people that create these things, however, as hours of research go into creating them, and it opens the gate for people that are less familiar with these ancient operating environments - I just have a hard time recommending something them for a first timer, and they're ironically better suited for someone who already knows the basics of DOS. They'll have a much easier time troubleshooting common problems, when they arise, as they'll know what to look for.
Anyway, this is just my advice. People are welcome to disagree, and I won't hold it against them.