Reddit mentions of Fusion Climb Aluminum Little Foot 4 Hole Rigging Plate

super late to this party but oh well:

If you are looking for something fun and packable I would suggest getting about 120' of balance communities regular feather webbing(the green kind not the pro), you won't be able to use it on highlines but it is super packable and a lot easier to rig than tubular and would be a great lightweight setup to have for traveling. plus you can also rig it primitive style pretty easily.

Once you do want to get a longline kit, it is hard to avoid the pully system. You can go on the cheaper side and get;

2* double pulleys (https://www.amazon.com/Fusion-Climb-Secura-Double-Aluminum/dp/B00P8D6H8I),

a rope grab (Petzl tiblock)https://www.amazon.com/Petzl-Tibloc-Ascender-One-Size/dp/B000AXTO8Q/ref=sr_1_1?s=sporting-goods&ie=UTF8&qid=1499726769&sr=1-1&keywords=tibloc,
a carabiner,

single pulley https://www.amazon.com/Lixada-Mobile-Single-Climbing-Rigging/dp/B01I10MMEM/ref=sr_1_5?s=sporting-goods&ie=UTF8&qid=1499726811&sr=1-5&keywords=single+pulley,

small rigging plate (https://www.amazon.com/Fusion-Climb-Aluminum-Little-Rigging/dp/B008KEDV36/ref=pd_sim_468_3?_encoding=UTF8&pd_rd_i=B008KEDV36&pd_rd_r=9GSDV5MPNYH1V1ND0S8N&pd_rd_w=FUuA4&pd_rd_wg=eWUeb&psc=1&refRID=9GSDV5MPNYH1V1ND0S8N)

and about 50-60' of static rope (https://www.amazon.com/GM-CLIMBING-Double-Accessory-Fluorescent/dp/B01H5CY7SQ/ref=sr_1_3?s=sporting-goods&ie=UTF8&qid=1499726145&sr=1-3&keywords=static%2Brope&th=1&psc=1) this should work fine for you and is rated to 19kn.

The most expensive part of this pulley system is going to be the brake. I would recommend a gri gri just as the simplest option and with longlining stuff like this you should be okay getting a used one off of ebay, just inspect it well before use to make sure there aren't any defects or anything. You could go ahead and use an ATC and tie the tail off but I suspect you would lose a lot of efficiency in this already pretty inefficient but cheaper set up. You can also go ahead and get the slackbro's pulleys, they aren't the best, but they are so bomber and are still nice to have around after you are trying to upgrade and may be easier than trying to piece everything together.

When it comes to webbing, that option is kinda up to you, try and make some friends with local slackline groups and walk various types of webbing and you will find what you like best, I would recommend getting 100 meters for your first length though, it's not too much to haul around and when you start rigging highlines longer than 50meters, there should be plenty of people who also have 100 meter lengths that you can partner up with.

Also keep an eye out on slackchat used gear group on facebook, you can usually find some pretty decent stuff on there.

Good luck and happy slacking!