As a beginner you'll want to get a slingshot that feels right in the hand and can be held comfortably in the style of shooting you prefer. Meaning if you prefer the slingshot to be held in an upright position with a hammer grip... get one that has low enough forks so that you don't get to much strain against your wrist and has some wideness to the lower handle where the ring finger grips to help with slippage.
If you like to shoot in an upright fork position with an index finger/ thumb support grip... get one that is not to wide through the forks so that you can comfortably extend to reach easily and naturally.
If you think shooting with the forks to the side (gangsta) is the way to go... then get yourself a slingshot that accomodates your hand size and grip but also consider the torsion of the wrist at the same time... a canted handle with an ergonomically designed frame may be an option here. Just pick up a pencil, put it in your hand, close your eyes and extend your hand like you're holding it in a sideshooting hold... relax the tension in your wrist and forearm, open your eyes and see the angle created... find a slingshot that can achieve that angle, usually 10-15 degrees off horizontal yet have the bands line up perfectly up and down on top of each other.
Okay, if you have a weak wrist and or grip... consider either getting stronger, or going the wrist braced route. If you look at the wrist braced models think about the method you aim with and then buy one that fits you the best... look through slingshot ads on ebay... see something that just seems like it'd fit you right, then find a quality product in that style.
Now, all that said... it doesn't matter even a little bit which slingshot you make or buy if you don't have the right elastics and pouch to suit you as well.... some people shoot well with and prefer tubes, either single per side or multiples depending on philosophy. Some people like and prefer squared rubber. Some like and prefer tied (chained) together rubber bands, like you use in an office setting. And some people prefer flat bands, gum, theraband, latex etc...
Each elastic propulsion system has pros and cons. Tubes are usually more resiliant and longer lasting than flat bands, and readily available at many stores but are not the fastest on the snap back. Chained rubber bands are extremely readily available and cheap, yet are not all that long lasting. Square rubber is not readily available in the USA and doesn't snap as quickly but it is tough and long lasting... Flat bands are usually the fastest, can be found fairly readily by simply cutting your own from exercise bands, are not that expensive if you cut your own but usually don't last as long as tubes.
If you were to make a comparison between elastics and cars... you could say the rubber bands are like Yugos, square is like the VW, tubes are like the Ford Mustang, and flats can range from less than a Mustang to a Ferrari depending on cut, taper and material.
Which ever elastic suits you the best... you need to make sure it's attached well and the force is symmetrical for both sides.
The pouch... material... leather is the go to material. Supple and strong are keys here. It must be able to grip the ammo yet release easily... there's some other materials that may work fine... just don't worry with them right now though... go with leather. Five ounce, smooth on one side with the suppleness of thicker driving gloves works very well.. it'll last a long time and will grip/release right too.
Wet formed ball indentions, centering holes or just a flat "utility" pouches all work well and you should experiment with which one suit you the best.
Just keep in mind... There's a scene in the classic movie, The Good, Bad and Ugly... where Tuco goes into a gun store to get a pistol. He takes parts from several different new guns and ends up assembling "the perfect" pistol to suit him from the parts.... MANY people do the same thing with slingshots!