Welcome to the addictive world of home brewing!! As a newer brewer myself, I know right where you're at. Here's what I've found recently.
Mini mash just requires a little more temp control than "boil, add hops, cool..."
I chose to mini-mash my second brew, mainly because I wanted to understand what was involved in the beermaking process and make sure I could follow the basic steps, learn where to stage everything in my small kitchen, etc. Basically, all mini-mash entails is another 45 minutes of cook time over all-extract. Put your grains (generally 4ish lbs) in a mesh bag and steep them at a constant temperature (generally 155*F). Once you figure out your stove setting for maintaining the temperature, all you need is to grab a pair of tongs and swirl the bag around some every so often so as not to burn the grains on the hot pot bottom. The guy at the LHBS said it was just like making tea, and I think that's a pretty accurate description.
Still, I would recommend a standard extract brew for your first batch just so you can see how it all comes together. If you're feeling adventurous, try your hand at making a yeast starter for your brew. I feel it made a big difference in the amount of fermentation in my second brew compared to just pitching the smack-pack into my first, not to mention how quickly it took off from when I pitched.
And there's nothing wrong with going just two weeks in a primary fermentor for your first batch. Adding a secondary gives the new brewer more opportunity to contaminate his beer. Don't get me wrong, I'm not trying to scare you into doing something if you're capable... but I think many folks here would at least recommend a glass carboy or a PET bottle for a secondary. If I'm not mistaken, the Poland Springs bottles are air-permeable, and leaving your brew in that for a couple weeks might let unwanted air into your brew. Many great brews have come from a single-fermentor setup.
1st brew - all UNHOPPED extract, make a yeast starter, add your own hops at the right boil times, 2 weeks in a primary. Learn the ABC's.
2nd brew - mini-mash, and use a glass secondary. a 5-gallon carboy shouldn't put you back more than $25-$30 at your LHBS, and it'll last you many many batches.
Disclaimer: My feelings will not be hurt if you differ from this advice. Just let us know what you did and how it turns out