Self hosted blogs would be the best option as you have control over every aspect and don't have to worry about getting banned. Also, a .com domain name will in most cases be favored in the eyes of Google more than a subdomain.
It all comes down to if you can afford the monitorial investment or not. Having a web 2.0 blogging network (blogger, wordpress.com etc...) will be free, but if you use custom hosted domains you have to pay hosting and domain registration fees. A blog network of 30 domains would cost about $75 a month to maintain ($300 a year/$25 a month on domain registration and $60 a month on shared hosting), this is not including content creation which could cost you way more.
Personally, I would create a free network using web 2.0 blogging platforms until I start making enough money to completely cover the self hosted network maintenance fees.
I'm glad you said your not going to rush the creation of the network, the key is to take your time and not leave any footprints or raise any red flags (same Whois, HTML similarities, same web hosts, same themes, interlinking, crap content).
Here are some resources that should help you out:
Basics of creating a network:
http://www.blackhatworld.com/blackh...-ranking-blog-network-rank-anything-ease.html
http://www.blackhatworld.com/blackh...trol-your-own-search-engine-optimization.html
http://www.blackhatworld.com/blackh...p-private-blog-network-linkbuilding-time.html
http://www.texfly.com/build-a-blog-network/
List of footprints to avoid leaving:
http://www.cloudincome.com/private-blog-network-footprint-checklist/