If you shut down power at the cottage, or at least fully unplug the receiver, it will cease receiving the monthly or so key updates, so need them refreshed first use in the spring.
I do have a couple older receivers I occasionally use (315, 505), and if I lave them unplugged for months, they lose authorization next time I try to use them. Leaving them plugged in for a couple weeks brings them up (I am patient).
I think 6 receivers is a general account limit on active receivers. Most single households should never need more than six. I doubt you will be affected adding 630 (or probably replacing one receiver), but I cannot guarantee that.
You will need anew LNBF on the dish, or in your case both the cottage and home dish, to receive the new channels from the G1 satellite. Each receiver has a go around getting the v-code updated. Only the 6xx receivers will get the G1 programming. The simple terminology is G1 is the new satellite, X-Ku is the LNBF you need to receive it, V-code is basically a code to receive a channel map, which contains the parameters the receiver needs set to to tune channels, which can vary based on what LNBF you have.