Yeah, 100 might not sit well with you. You could easily separate that into two separate sessions and just work on your smoking technique. If you use less cannabis and take a single long, slow hit and hold it, you should be fine. You can easily get as far as you need in a hit or two if they're good enough. Some people find that cannabis can make the trip less intense or the visions harder to see, though for others it is the opposite. You may want to experiment with this to find what's best for you.
If you do want to have all 100mgs at your disposal, there's no problem with this so long as you do it safely and proceed at a pace that is comfortable for you... but loading the whole .point into a bong bowl may give you far more powerful results than you are prepared for. You'd want to be careful in how you smoke that much.
I'd recommend infusing the DMT into a bowl-sized portion of herbs. This allows you to take comfortable hits from a bong or pipe and estimate about how much you're smoking, and also tends to ground the experience in a non-limiting way that can help you in the process of familiarizing yourself with the drug and your interaction with it. You can do this by just dissolving your portion of DMT in a small amount of a solvent (such as solvent for extraction) and wet your herbs evenly with the solvent, then allow to dry completely. This is classically done to great effect with the leaves of the ayahuasca vine, but you can use cannabis or any other non-toxic herb that you enjoy smoking. This can also enable you to take multiple hits over a longer period of time, extending your trip.
Please remember that the only safe way to use this stuff is to be mindful of yourself and your environment and to slowly familiarize yourself with how you interact with the drug and then dose yourself accordingly. This stuff can be indescribably strong, unfathomably deep and almost impossible to make heads or tails of. Nothing can prepare you for the experience but the experience itself, so make sure you know where your feet are before you take the next step.
Happy Travels
Hg