Horticulturist is a broad term for any type of plant and soil expert. An arborist, meanwhile, specializes in all aspects of tree care. You should hire an arborist when you need assistance with tree-related tasks, such as pruning large trees, removing trees, diagnosing a sick tree, or emergency tree services. Horticulturists aren’t qualified to handle those types of tasks.

It depends. Smaller, younger trees take longer to mature, but they're more resilient, their roots don't get as damaged during transplanting, and they recover faster. Plus, they're much more affordable to plant, and it's possible to DIY the planting. 

On the other hand, mature trees produce fruit faster and provide more shade and privacy immediately. Ideally, a small or medium tree is the better choice if you can wait a few years for it to mature. But if you need immediate maturity, a larger tree is the only option.

Planting trees far enough from your foundation will protect your home from root damage, but if you’re dealing with existing trees, you can still guard against roots. Root barriers form a physical boundary that will prevent roots from encroaching on your foundation and can help save you from expensive foundation repair costs.

No. Topping a tree refers to severely cutting down all its major branches and tree in a straight line. It was once recommended for streetside deciduous trees but has fallen out of practice. Topping leads to many problems, removing so much of the tree that many trees struggle to survive and become much more vulnerable to insects and diseases. Also, it doesn’t really help tree growth as once assumed and often leads to an ugly appearance of many sprouting stems in competition to become new main branches.