Cables are electrical cables, I use 1 mm²/17 or 18 AWG, you don’t need anything bigger. Just buy a small roll of flexible 2 core, cut it up as necessary for all electrical connections on the 12v side. For power to the power supply, I’m sure you will have an old cable for a PC or something, or just use a 3 core flex and stick a plug on the end. Length used is up to your needs.
String is for hanging, look for 1/8th inch SISAL string as that is more flame retardant than the nylon crap.
Metal plate doesn’t have to be thick, 1mm is enough, 9.8m of strip needs a minimum of 35cm/14" x 28cm/11.25" because the flexible strips can be cut every 5cm/2" so it works out best at 28 pieces 35cm in length which are 1cm wide. That gives you a plate just over 1 sq.ft with all these leds on it. That’s the minimum, you can go wider if you want by leaving space between the strips so they cover a bigger area. The choice is yours, since you are not tied to specific lengths like with the “solid” strips.
Timer is just a standard mechanical plug in timer, they only cost a few bucks.
Tent? No idea, don’t use one when I have a nice little utility room where conditions can be controlled.
Fans. You can use clip on fans, desktop fans, fan/heaters, whatever. As long as 1 can blow nothing but cold air then that’s the important thing, which is why my “high” one blows cold 24/7 and the “low” one can either blow for circulation or be used for heating in winter.
Heaters. The world is your oyster there IF you need them. You can use fan heaters, not blowing directly on plant, convection heaters (be aware they will reduce humidity so can cause issues if the air gets too dry), oil filled radiators, whatever. Just figure out what fits your needs best.
You will also need pH/TDS pens, there’s a section on them here so you can see what is recommended as everyone has their own choice and opinion on what to get.
The potting compost I use is Agrofina Bio Nature, a fairly low NPK mix which I add Perlite to, and hydro balls on the bottom of the pot to help drainage. You’ll find something as “soft” as the stuff I use, and the plants love it when you just drop the seed straight into it because of the composition of the compost without lumps of wood and everything in it. The feeding I use is not cannabis specific either, and some here will tell you to look for feed for tomatoes.
Basically, the only thing I use that is specifically for cannabis is the seed. You’ve seen the pics, and before this latest adventure I had an Acapulco Gold under the panel which cleared 3’ in height before I drowned it (a HUGE part of the learning curve). All the parts of my grow setup seem to be working quite well, except for the two-legged idiot who makes mistakes, which means that, for me, it’s perfect for learning the art of growing before splashing out a “decent” amount of money on something that will do much, much better than what I have now.
Oh, obviously a temp/humidity meter is essential, you need to know what is happening in your room/tent so you can adjust as necessary. Too warm? Stick a big cola bottle of water in the freezer for a while then put that in front of a fan. Too cold? Obvious. Too humid? Get some of these cheap dehumidifier packs for cars or for where you have humidity problems such as where washing machines and driers are.