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I purchased a bike which I believe to have tubeless tyres and I had a few basic questions:
The reason you'd want to remove the valve core is because you need a rapid inrush of air to seat the tire properly on the rim's "shoulders"; also one method of adding sealant has you inject it through the valve stem. A lot of regular innertubes have removable valve cores too.Since no-one else mentioned it, a quick answer for point 1.
If you give the wheel a shake near your ear you should hear sealant sloshing around - if you don't hear it, or it sounds like very little, its time to top up.
I will add a bit of detail to @AdamRice's answer on a couple points.
You can physically check if you have sealant. Some tubeless sealant bottles are sold in kits with a little dip stick. You'd remove the valve core, and dip the stick into the tire. This is rather similar to checking the oil in your car. Another way to know that your sealant has dried up is if your tire deflates itself without any apparent reason. This happened to me this winter on my gravel bike, which I'd mounted on my indoor trainer. Also see MaplePanda's comment, but do note that I'm not sure if you need something stronger than a standard floor pump to reseat the bead of the tire.
Focusing on what you use to inflate your tires once they're seated, you can indeed use any pump including a mini pump if you have the patience and arm strength, or an air compressor, or the air compressor at a gas station if you have a presta to schrader adaptor (and preferably a pressure gauge). If you were possibly thinking about what to use to seat the tubeless beads on the rim, this is where you might need something other than a regular pump, or else you could pay a bike store to seat your tires. You can use CO2 cartridges to seat your tires also (but possibly not to inflate them with sealant, as the CO2 may react with the sealant). This might seem wasteful if you are swapping tires a lot, but most of us probably aren't doing this, and you may only change tires out annually or less frequently. Alternatively, some floor pumps come with a separate air canister that stores compressed air to seat tubeless tires. I know that consumer air compressors have been coming down in price, and they can be used for this as well. They can be multipurpose, e.g. inflate car tires, use for cleaning parts. Cyclingtips had a recent review on the subject.
I think that valve core removal tools are often built into many newer multi-tools. You can also get them standalone. They can be as simple as a little piece of molded plastic that fits around the flats of the valve. A standard pair of pliers won't grasp the flats on the valve core precisely, but I believe they will work in a pinch. They're a great thing to have handy if you run tubeless tires. If you are converting to tubeless tires, I would recommend checking your multitool, and stashing a standalone valve core remover in your saddlebag if you don't have one.
A minor digression from point 3: say you run deep aero wheels, either regularly or as event wheels. You can buy tubes with long valves, but I think it's more common to buy valve extenders. If you are planning a flat kit and your spare tube has a standard length valve, I'd recommend keeping at least a valve core tool in your repair kit, and possibly a spare valve extender. It is easy to forget this little detail, particularly if you run deep wheels only for special events. This applies if you run them tubeless (because you want to have a spare tube anyway) or with inner tubes.
