My personal experience (former piper of the Highland variety) is that you have a great advantage in having played the big pipes, as opposed to other folks who haven’t.
I can’t speak to the advantages of having learned the flute, but it certainly couldn’t hurt knowing some Irish tunes ahead of the UP.
brianc is, in my observation, correct. Someone playing another type of bagpipe, especially another type of cauld wind pipe has the easiest time in picking up uilleann pipes.
Playing the flute and highland pipes should give you a pretty good head start.
The bellows will take getting used to, but you will get used to it, and then it’s not hard to handle at all.
The bell note is D, like on the flute, but you’ve got seven holes in the front of the chanter, plus a thumb hole for back d. I dunno how that relates to the highland pipes.
There are fingering charts all over the place, here’s one: http://www.howardmusic.co.uk/club_f_chart.htm