Welcome to Sailnet. I'd highly recommend you read this POST
to help you get the most out of sailnet.
A couple of questions....
First, how much sailing experience do you have?? From your OP, I am guessing you have little or none. Taking lessons is a good start... as is spending some extended time on boats. Finding out if you're prone to seasickness is something you'd rather learn sooner, rather than later...
Second, how much do you know about what is required in maintaining a boat and what kind of skills do you have towards that end. Given your OP, I am guessing that your funds and income are somewhat limited... I would also point out that you should generally reserve about 15-25% of your purchase price for upgrading, refitting and repairing whatever boat you get. While this may sound a bit high, getting a boat to fit the way you want it to be is not an inexpensive process.
If you're single, I would look more towards the 30' end of things... The reasons for this are simple. First, you're far more likely to get a decent boat in decent shape than if you go larger. Second, you really don't need much larger a boat if you're serious about living aboard as a priority. There is a blog, weliveonaboat.com, which is about a family which started on living aboard on a Alberg 30, as a couple and a toddler, but has since moved to a larger boat, due to having another kid or two. Third, the slip/moorage/maintenance/haulout fees will all be lower with a smaller boat.
I would highly recommend you look at James Baldwin's Boat List
. He's got a lot of nice boats listed there that are very capable, and reasonably inexpensive. There are many coastal cruiser type boats that you could also pick from, but if sailing is your priority, I'd go with one of the beasties on James's list.
I'd also recommend you read Sailingsimplicity.com, which is the blog of one of the members here.
Finally, I'd recommend you purchase David Seidman's book, The Complete Sailor
, which is about $16 at the local bookstore. It is very well written, has good illustrations, and covers a wider range of sailing related topics than most introductory books.