Fullframe or APS-C

It is about the size of the image sensor

A full frame sensor is 36mm x 24mm and an APS-C sensor is smaller, about 24mm x 16mm. While a bigger sensor is better, cameras with full frame sensors also costs more, requires larger lenses and as a result also weighs more.

APS-C on the left and Full frame on the right

Of course full frame is better but APS-C is perfectly OK

I have owned and used multiple full frame and APS-C cameras. I have absolutely no problem in picking an APS-C camera for a trip. In fact I usually combine APS-C and full frame cameras for my photo trips. Almost all DSLR cameras manufactured in the last 10 years or so are really good.

Here are things to keep in mind

Cost: Full frame cameras cost considerably more than an APS-C camera. This is not only the camera, but also the lenses that are designed to work with full frame lenses are larger and more expensive. Part of this is also quality. Equipment for full frame cameras is targeted for professionals that need the additional edge in quality.

Weight: larger sensor, requires a larger body, and needs to be coupled to a larger lens. All of this add to the weight you carry. Once again, quality plays a role. More premium lenses are available for full frame cameras which are also heavier.

Quality: a larger sensor can translate to more megapixels or more sensitivity or a combination of both. When compared to a contemporary APS-C camera, a full frame camera will have measurably superior quality in pictures. However, this does not mean the pictures will be visibly better. A lot of the quality difference will be in places that most amateur photographers will not realize.

As I explain in most equipment is more than good enough, I love my Nikon D850 that costs more than 2'000, but I frequently pick a used Nikon D90 when going out.

Summary

If cost is not so much of an issue, by all means go for full frame equipment only.
You will not suffer if you have an APS-C camera if cost is an issue. Anyway you will end up paying more for your lenses than your cameras.
You can start with an APS-C camera and later add a full frame camera, just make sure that you choose lenses with this in mind.
Actually the camera body is not as important as lenses. So if you want to have more freedom check the selection of lenses that are available for the body you are looking for. Recent mirrorless systems from all manufacturers actually market and target full frame sensors more aggressively, and there seems to be less choice for APS-C specific lenses engineered for recent systems. As an example, for a DSLR Nikon at the time i write this (Nov 2021) there are many lenses for APS-C systems, but only three dedicated lenses for the Nikon Z FC APS-C mirrorless camera.

These pages are for Amateur Photographers and not really for seasoned photographers and professionals. I have no affiliation or commercial interest with any brand/make. I write from my own experience. I ended up using mainly Nikon, so I am more familiar with this brand than others. See price for notes on pricing as well as photography related links.