Normal DIY types don't have access to over 100 mg/ml nic base, 10% nicotine, and it is readily available down to 36 mg/ml. Since some pre-mixed eliquid is actually available at 36 mg/ml, at least the lower concentration nic bases really aren't that big a deal, one needs to follow some pretty simple precautions.
Overall, DIY absolutely isn't for everyone, and as one works with the higher concentrations basically more care has to be taken in terms of proper cleanup, use of simple disposable gloves and/or safety glasses is recommended. I rarely work with 100 mg/ml, it's just easier to work with larger volumes, though I keep some 60 and 100 for making 24 mg/ml and higher strength eliquids.
Even for lower strength final eliquids, everyone should take care to keep them inaccessible to children and pets. A lot of the things I make smell nice, I wouldn't want a child to drink them.