You'll need to fill out your location so we can help you better.
If you're from canada, then be aware that you cannot purchase from retailers overseas, they must be bought from canadian retailers, or else they will be seized at the border, and you'll be blacklisted.
A suppressor does not work in airsoft like it does it real life, or at least nowhere near the same. Suppressors in airsoft depending on their make, will dampen the sounds a little bit, but not enough to make a huge difference.
Depending on the area you're in and their by-laws, it is illegal for you to discharge any type of firearm or airgun. Shooting around in the backyard may not be the best course of action.
The TM mp5k is good out of the box, I cannot vouch for the other two. I believe Schwag managed to make a galaxy mp5 a monster, however he is a very good gunsmith and knows what he's doing. I'd personally go with the TM, buying cheap means buying twice, and TM is good quality stuff.
Please keep in mind the prices you see on international retailers are not what you'd find in canada, so finding a "cheap" mp5k may be impossible. We also cannot advise you on where to get one until you've proven yourself to be 18. You can read up on Age Verification in the FAQ's, which will give you access to Airsoft Canada's classifieds section which opens up a huge avenue for airsoft in canada.
So please fill out your information a bit more, and take some time to go through the FAQ's on age verification, importation laws, and prices of airsoft in canada. By reading through these, you'll be able to ask more specific questions and get good answers.
Enjoy your stay.