Electrical – Joining two 10mm twin and earth cables

There are tools which do the job for you. They will probably take a little adjustment when first used, but then they're fine. They are literally the easiest way to consistently strip mains cable.

Many years ago my father had a hand-held tool explicitly for stripping Australian 240V household wiring cable. It had two clamps, two blades and a two-part action. The first clamped the cable and made the cuts, the second separated the clamps, neatly stripping the end off the cable.

(I should add that I don't strip cable every day but I learnt how to use a small but very sharp pen knife to strip outer sheaths. A bit time-consuming, but I like doing it that way as it works on any sort of multi-core cable. And the trick to not nipping the conductor is to not cut quite all the way through the insulation: let the stripping effort break the last little bit.)

To answer your biggest question: I'm pretty sure it's not code-legal to tap into the feed from your meter panel with split-bolt connections. It's possible that your breaker panel has some lugs near the bottom of the load side bus bars to connect a feed to a subpanel, but most don't.

So a possible solution is what Doxy suggests: a new 100A panel that feeds your existing panel as a sub-panel. Before you consider that, I'd check to see if your panel type admits half-size tandem breakers. These are breakers that fit two half-size breakers into the space for one normal breaker, and this would free enough space for a 40A breaker to your EV charging circuit in the garage.

Another possible difficulty, though, is that your 100A service is awfully marginal for the addition for a 40A EV charging circuit. Although you didn't give all the relevant details, I assume your 1000 sq ft house (does this include the basement, if there is one?) has an electric dryer. In my jurisdiction, a load calculation shows you would require a 107A service. You may be able to get away with a 100A service, but it will depend on your inspector/permitting authority.