Hi Lexie and welcome to the forum,
Provided that the soil the ficus will be in does not dry out, it should be fine for two days. My advice would be to water thoroughly before you leave, then place the tree completely in the shade. This will not harm it at all, but should help stop the sun evaporating the water out of the pot. The lava rock/mini mulch will drain well, but should retain enough moisture for the weekend in summer temperatures. Putting it inside with a humidity tray will also work well. It might be a better option, as believe it or not, bonsai trees are quite often stolen, so if you are spending a fair amount of cash on one - I'd put it inside.
Taking it with you for the week shouldn't be a problem either really. They are very forgiving bonsai plants, and can tolerate low light levels and a fair bit of neglect. If you are moving it from the garden of your home to the garden of your cottage, it won't bat an eyelid, just be careful that it doesn't get damaged in transit.
Some species of ficus are easier to care for and train as bonsai. I have a ficus retusa "Tiger bark", which I think are also called ficus "too little". It doesn't mind being pruned or wired and would recommend it to you.
You might also wish to obtain a copy of a highly acclaimed book by one of our very own forum members, Mr Jerry Meislik, as he is pretty much the authority on ficus bonsai. Here is a link to his website
www.bonsaihunk.us
Hope that helps.
All the best,
Aaron