Welcome to Shetland cattle! We even have a Shetland cattle board on TAS!
Is it two heifers you're getting? Who are you geting them from?
We did what you're doing- bought two six month old heifers in October 2010, housed them through the winter and halter trained them. Had our first calves in 2012; we now have one of the original two (Blizzard), plus her 2013 daughter (Annie) and her daughter's 2014 daughter (Rosie) plus Blizzard's 2016 daughter, Winnie (who we'll be selling I think, when she's weaned) plus two 2015 steers (robbie and Fraser) and two 2016 steers (Paulo an Pedro). We've also bought a bull calf, who we'll be getting thsi month. Blizz and Annie are in calf and Rosie might be.
We have two beasts (a 2013 steer and a 2013 bull) hanging at the butcher's just now.
We sold the other original with her two daughters and a bull calf at foot last year as they didn't take to hand milking.
I'm not sure about the putting them out and bringing them in - if it's wet underfoot, they'll make a mess of the grass and eat any that's growing. Personally, if they're in, I'd keep them in. They don't fret.
Ours like sugar beet - in fact they like anything in a bucket - and it's a good way of getting them on teh halter. If you can halter train them, it will save you hassle later.
You'll love 'em.