They are tropical and I think they would do better indoors - not just a cold garage. Normally they should in kept in greenhouses which are not available to a great many of us. In winter tropicals do go into a form of hibernation and so expect that they would look poorly in the winter months but they should recover in late spring when they are taken out once more.

Spider mites, scales are probably what you need to look out for. Mist the foliage with water every once in a while. Use cotonbuds dipped in rubbing alcohol for scales. Do not fertilze during winter and water but do not overdo it.

Re: replanting bare spots. Is this topiary formed by plugs of figs? If so, wait till late spring to fill in the gaps. Or let the other figs branch out and cover the spot. They do grow slow but they do send out branches to cover large areas. In Asia, where I used to live, these are used to cover concrete walls of properties. Akin to ivy growing on the side of buildings - except the these plants remain evergreen. One plant can provide coverage for approximately five square feet