1) Most kits that I've seen offered aren't fused. I make them - and I'll fuse them if you like.
2) The Anderson connectors (that's what are typically used) are quite rugged. I've run them over with my truck before without any significant ill effect.
3) Note that you can use the Anderson-style connector to connect various accessories as well. I can get SB175 (for 175A housing - medium) connectors to accept anywhere between 4AWG and 0AWG wire, and SB50 (for 50A housing - small) to accept something like 10AWG-4AWG.
And, I also have PowerPole connectors in 30 and 45A, which can be ganged into whatever configuration you want. I'll sell those as kits, but I prefer to terminate the SB series myself, since they take a fairly heavy crimp and I want to make sure it's done right (I have tooling to do it correctly, left over from when I was an industrial mechanic.)
In fact, I recently did a custom kit for a fellow (on this board, I think) for dual batteries, isolator, winch wiring, booster cables, SB175 on the front bumper, and I think he's still thinking about adding an SB50 for low-draw accessories later - it's entirely up to him, and I'll do it if he wants me to.
ANL fuses (which I typically use for high-current loads) are rugged little numbers, and are available up to 600A with a little looking. I'd probably stop at 200A for fusing booster cables, tho, unless you make a habit of jumping Diesels. Most gasoline engines top out at 200A or so cranking current, and you want to give it a minute or two to charge the battery before you try to crank the started vehicle anyhow. I have, so far, sourced fuses up to ANL350. I've seen them up to 600A, and I can probably order them, but it does get spendy up past 200-250A. Hit me backchannel if you want to discuss this further - JeepI6Power AT yahoo DOT com.
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"