How to help small furries is important, as most pet stores don’t know about welfare, so sell them without proper advice (big stores like Pets at Home still house social pets alone, showing they have no idea on how to house pets, nor advise others). Small furries and other creatures need as much knowledge on food, care & behaviour as other species.
Rabbits are social and get lonely alone (but if you house them together you have to ensure they are neutered or they could fight). Likewise, guinea pigs are social, but unless they have lived with rabbits from birth, they could get kicked and injured, and they also eat very different foods. Some foods you may think are safe (like potato peelings) can actually harm, so do read a good care manual. Small slices now and then of apples are ok (but not cores, seeds or stems: one or two slices is plenty. This post has great info on safe rabbit treats).
Rabbits obviously like to run outdoors, so make your garden safe for pets to avoid toxic plants (also for indoor rabbits: just brushing a bobtail against an indoor plant like sago palm could harm). Avoid cocoa/pine/rubber mulch (and fresh compost) near pets.
To help prevent attacks by birds of prey, stay with them and offer cover for outdoor pets to run to. The Spruce has useful tips on how to keep pets safe from birds of prey. In the USA, they have more issues, as there are much larger birds of prey and open land.
Rabbit Rehome & Guinea Pig Rehome both have small furries looking for loving homes. Ensure you have enough space and secure outdoor runs. Blue Cross has good advice on different small furries including hamsters (not a good first pet for children as they are nocturnal, and easily injured – they can die from exhaustion on wheels).
It’s kind to let pets run outdoors, but if you live near birds of prey, take care. The Spruce has useful tips on how to keep pets safe from birds of prey (saving their habitats would mean they are less likely to strike). In the USA, they have more open land and larger birds of prey.
Other Small Pets
Birds in cages are usually miserable, an aviary is better or even a parrot sanctuary (they fly 30 days in the wild). They have many dangers including cookware (heating those pans with red spots in the centre are lethal near pets, plus ceiling fans, pencil lead and more. GreenPan ceramic cookware is better but no cookware is safe near birds if you live with them, no matter what the company says. Pet Coach has a good post on the many dangers to birds including hairdryers).
Unless you already have them, don’t buy fish from shops, as most are from tropical homes and in poor health and welfare when they arrive. Looking after fish is complicated (heat, light, changing the water correctly). If you don’t have room for a big tank, consider giving them new homes to local hotels that may have kinder homes (be sure to change to the water properly, to avoid shock).
There are charities that re-home all kinds of fish (including in ponds) but they are full to capacity. PDSA has good information on caring for fish (including how to change the water safely) and also recommends vets that care about fish. If you keep fish outside, see how to build a garden pond and safer alternatives to netting (to humanely deter herons etc).