In less my eyes deceive me there is a gravel base in the bottom of the planter. I suspect this is over the subsoil the foundation of the house was built on. If so, there is no need to worry about drainage as the planter will be coupled with the ground making it a raised bed in effect. As for prepping for planting, repair the end of the planter if you have a mind to, or use some landscape fabric to keep your planting mix from seeping into the cracks. do not add anything to the bottom of the planter, as you are only giving up valuable soil volume and decoupling your bed from the ground.

As far as soils go, I would recommend you look at the 5 1 1 mix or gritty mix so often discussed in this forum, They really are good formulas and have a great deal of knowledge base here to draw from. The gritty would be my choice due to the longer life span and less shrinkage, but the 5 1 1 will be less expensive and easier to obtain the materials to build. Either of these mixes will give you great drainage and aeration while maintaining an adequate level of moisture.

This thread should help you get where you want to go:

http://forums2.gardenweb.com/forums/load/contain/msg112015049996.html?33

Filling that with gritty would be crazy lol, I even think that the 5-1-1 would be overkill if that is native soil below and it is in reality a raised bed and not a large container....

First dump a bucket of water in the planter and watch what happens . If it drains out your good to go. No need to fill in the crack either.
Fill planter with cheaper " potting soil" not "potting mix" and not low quality "top soil". You can mix in some compost if desired .

I agree with Dickie, some decent potting soil, some compost, and maybe some perlite mixed into lighten things up a bit and increase drainage. A small portion of regular top soil probably wouldn't hurt if cost is a major concern...