I started Ukulele playing in last August, so I have now studied ukulele about 6 months. I had guitar background.
Now finally I start feel comfortable. Yesterday I added Bmajor/G#minor to my sequence practice keys. So I now can play quite easy all basic chords in keys of 4 flats to 5 sharps. Meaning also to able to make changes fast enough, in normal tempos.
What I mean with basic chords? I give them as example in C/Am: C, Dm, Dm7, Em, E, E7, F, G, G7, Am. There are still chords outside major, minor and their dominant 7th chords that I need from time to time to look in the chord sites, depending of the key played in. Like sus, 6ths , major sevenths, diminished/augmented fifths, 9ths etc. But basic chords I have now covered. Also in those other 2 keys that I still lack the sequence practice knowledge from the total of 12.
To be a good strummer with ukulele one needs to be able to play the lowest available notes in every chord, to keep them nut close and to avoid some immediate from maybe guitar knowledge got barre/movable chords higher up the neck, if possible, in my opinion. To keep the chords at the same approximate level and the sound that way balanced. It takes a lots of chords to learn even with only those above mentioned basic chords.
I am not the most technically capable person, so besides knowledge I have needed also to learn physically to play the needed changes and that is still a work in progress. But I feel quite comfortable now. I seldom touch my guitar because my uke chord knowledge is now better. I guess that has been one aim with my uke practice that I needed to reach.