You mentioned that the bottom is sloped and that's a good start. I'm assuming that every point in the bottom of the planter slopes to an outlet - the more outlets the better. I'm also assuming that the slope is, at the very least, a 1.5% grade. If not, you'll have problems. Think about where the drains are and the shape of the planter. For example, if you have a single drain at the lowest spot of an 'L' shaped planter, water can get hung up at the bend. You may have to drill out more drains depending on the size and shape of the planter.
The fabric can indeed keep your soil in your planter, but over time it will plug with soil that you're keeping in and drainage will be a thing of the past. Once it's in, there's no way to go in and clean out the fabric.
The gravel may help with drainage at first but over time, soil will sift down and maybe next year, the benefit of the gravel will be gone.
The key to a long-lived planter is to keep water moving over the long haul. If the bottom of the planter gets mucky water won't move and you'll end up with anaerobic soil conditions and/or an environment that favors the pathogens responsible for root diseases.
Silt and clay will end up settling to the bottom and doing just that if you use a good old fashioned "import soil" which will typically fall in the sandy loam category. Your best bet is to use a high quality 'medium' sand with less than 6% silt and clay.
Organic amendment will help improve nutrient and water holding capacities. However, organic matter below ten inches in the planter can also muck things up and lead to an undesirable amount of settling as the O.M. decomposes(I would only put it down to 6 or 8 inches but other go a little deeper) so if your planter is deeper than 10 inches, fill the bottom with sand and then include organic matter in the top and do not exceed 80% mineral soil to 20% O.M. by volume. Keeping the organic matter% relatively low in the sand will keep the water moving and also avoid settling. The O.M. will decompose over time. If that O.M. is placed deeply and/or at too high a volume, the settling can result in exposed roots and planter flashing. I don't know where you are or what's available to you, but redwood bark is a nice long-lasting source of O.M. for these types of projects.