I would put a valve inside the house where the pipe enters. Having one at the meter wouldn't hurt, but doubtful how much value it would be. I'm not sure about type L soft copper, but type K ridged would be great. I understand that soft copper is sold only in large rolls, so it would be prohibitively expensive if you had to by 100 feet or more to use 45 feet. I'd opt for the heavier gauge anyway. I don't think there is much to gain by going to a size larger than the outlet from your meter. On a short run of 45 feet, friction loss will be too small to consider. It is my understanding that underground K copper is supposed to be brazed rather than soldered. (But, I'm not going to dig down 5 feet to have the joints redone that I soldered when I teed my irrigation line) The pros may have some opinions that differ from mine and I would suggest you listen to what they offer. Many of them are not around too much on weekends and holidays, so keep checking back the first of the week.