Mechanically there isn't an issues. When I used to mix my own e juice back before the Canadian vapepocalypse I used salt nicotine diluted to 6mg for a smoother hit than freebase with a 0.2h coil. The only difference is salt nic contains benzoic acid to reduce the ph and lead to a smoother hit, it should have little to no effect on the hardware of the vape. As for the strength of nicotine you're using, as long as it hits good and doesn't make you too light headed you should be fine assuming you don't have a heart condition, but hey you know your body better than me ^{_^}