Alright, I'm not going to tell you *not* to buy that thing, but since you haven't even built a MG yet and don't have much experience with painting I'd probably recommend against it. Here's why:
1) Resin typically comes completely uncolored. Even the ones that do come colored, the color is mostly there for painting reference sake and the color itself looks quite poor.
2) Resin kits have very poor color/part separation. This means you have to have quite a bit of confidence masking in order to get the paint job you want.
3) Building resin is not at all like building a model kit. They are not snap together and require you to drill holes, pin the parts together and glue everything. It's a new, and frankly pretty difficult process to learn.
4) What you're looking at is a recast. What this means is they take a design that's be done in limited numbers by one resin artist group, cast it, and then make many more at a far cheaper price. This often leads to loss of detail, warping of parts, etc. All these problems are fixable, but require a bit of learning to figure out how to do.
5) Resin is typically very heavy. Even when put on a nice MG frame, it's often difficult to get it to hold a pose without pinning/gluing joints into place. If that ZZ can hold that giant cannon unaided without fusing its joints, I'd be very, very surprised.
That being said, if you feel like you're up to the challenge, and want to learn, resin kits are quite fun. It's way more of an art project than your typical gundam kit. The site you're looking at is one that's known for its high quality recasts, so the problems you have to fix should be fairly minimal. That kit also uses a real MG frame, which is something that's certainly nice. I would then recommend you practice your painting (particularly masking) on something like small SD kits so you know what you're doing before you go in. You also should probably build a smaller resin model first. I'd probably recommend some sort of weapon like this
http://www.gkgundamkit.com/en/shop/products/240mm-bomb-gun-sniper-laser-cannon---d793bb7d0-0145-428b-b795-41e0318de220.html to learn how to work resin properly before moving onto a more expensive kit.
Let me know if you decide to go forward and I'll try and compile a list of all the resin tutorials I can find. Resin kits are absolutely gorgeous once you learn how to put the work into them, but it's certainly a task to undertake. If you're willing to put the work into them, you can get amazing works like this.
It's a lot of work, but resin is really rewarding when you learn how to work it.
Damn, now I've made myself want to buy that GP-01.
