Oh dear, we're all on a right downer at the moment, aren't we?

(must be lambing induced lack of sleep!).
The main reason I struggle to make my wee flock break even is economies of scale (having to buy big bottles of meds and then waste half, having to buy feed by the sack rather than by the tonne, etc). I think your Dad could be key to making this work though Megan, and that could give you a leg up compared with the rest of us.
I take it you'll be renting land from your Dad or another neighbour to begin with? In which case, most of the expensive things like trailers and hurdles are going to be available to you when you need them for free or cheap, right? Also, could you do a deal with your Dad to share medicines etc with him, at cost? If you were my daughter, I'd want to encourage you to do that, and would gladly give you a start in return for some help (e.g. you help me to gather my sheep for shearing, and then we'll do yours at the end).
As for a breed, that question almost never works out on forums like this - we all end up recommending what we keep ourselves! Instead, why don't you have a chat with your Dad, and with other local rare breed people, and see what takes your fancy from the
RBST watchlist.
Perhaps you could even cross your sheep with the ones your Dad keeps?
Anyway, there are loads of ways to make this work. Do think about the practicalities, but also think laterally, think about adding value, and think about what you need to do to make this fun. Also pick the sheep you and your boyfriend love - it has to feel worthwhile when you're heading out to feed them in a howling gale in the dark!
All the best!