You have 7 people, so if you took a week each you'd have a schedule of 6 weeks of "regular" work and 1 week of support.
And allocate some time to reducing that learning curve - a 3-4 month ramp-up is pretty extreme, so there must be work you can do to lessen that considerably. Whether that's through automation, bug fixes, documentaion, adding features so customers can self-serve instead of having to resort to support, it'll probably take some time to figure out the most effective combination of all of the above.
The same goes for the amount of support needed. A full-time role in a team of 7 is also pretty extreme. What is it about your company/product that needs so much? There must be things you can do to bring that down by an order of magnitude.