After playing guitar for 30 odd years, I decdided to take up mandolin about 18 months ago. To add to the problem, I was almost exclusively a finger picker rather than a plectrum user.
Since I play mainly Irish music, I took my lead from Andy Irvine and tuned the mandolin GDAD (low to high). Since I was used to various open tunings on the guitar, I found this mandolin tuning to be pretty easy to understand.
The main problem came when I changed from one instrument to the other. The difference in scale was staggering and it took me some time to get used to it but it comes with time. Stick at it. Mastering it is something else again.