Hi Maria welcome to YT! Lets see if I can help with some answers for you..
1. yes, yorkies will run and FAST. If it is possible to block access to the door by keeping your dog gated in other rooms that would be best. Training is essential.
2. 5yrs old is younger than many breeders will allow for yorkies in the home. If you do find one, try to make sure it is a larger, sturdier dog and always monitor their interaction.
3. Fence costs vary greatly by size, type and location. ex-pens are an affordable temporary solution for outside play time.
4. A good start is reading good info here, the site
www.buyingapuppy.com has good questions to help you interview breeders and the
www.YTCA.org has a list by area of member breeders.
5. Minimum age for a pup to be released to a new home is 10 weeks, though 12 is better.
Hope this was helpful.