Connecting nichrome wire to copper wire
It would be better to use a crimp because the nicrome wire could get hot enough to melt the solder. There are also crimp on lugs (that go to a fastener) without plastic that could melt that would probably be a better option (or remove the plastic). It really depends on how hot you plan on getting the wire but at 70 deg it probably wouldn't be that big of a deal what you use. Solder melts at over 200C so 70C would be fine to use solder.