I have bought/sold silver coins. I had planned to get into gold but just never pulled the trigger.
Buying: You absolutely want to buy from a reputable supplier. Apmex is where I would go. They are transparent with prices right on the website. You can see the difference by volume and if you would rather use a credit card (which is silly because of the fee). They are not consistent at giving buy prices, however and you would have to call for that.
Apmex does, at times offer free shipping on amounts over some set $$. If you are selling back, of course, you pay shipping.
I have sold both to a local wholesaler and to private people found on Craigslist. Private sales will bring in more money. Ask before you meet what they're paying. Set up an initial small amount and then meet. This is harder to do with gold than silver as it's tough to have only $300 in gold, where for silver, that's a small bag of quarters.
For storage, I would suggest a few things. First, don't tell anyone. Don't tell your wife or your dog or your neighbor that you even have gold. Buy a fire safe key lock box and leave it where any thief will find it. Put things that seem valuable in it but have no real value. Maybe some recent dimes, penny rolls, costume jewelry. Then buy a small safe that you can both hide and bolt to concrete. You want this hidden. As an example, the safe is bolted 3 feet up on a basement wall with shelves in front of it. Fill the shelves with crap you're storing. If nothing else, this will make it harder to find for a thief in a hurry. Any safe can be broken into, so I wouldn't bother with a plutonium grade kryptonite encrusted bank safe. I mean, guys have chained their truck to an ATM and dragged it away.....
Back to what to buy. You'll see that what you're buying will be priced based on various things. The bars...Apmex or Credit Suisse and the like are cheaper than coins. Part of the reason for that is that they're less desirable than coins. Things like Krugerands and libtards and mexican gold have different amounts of gold in them. Know what it is. I find that US coins tend to be the highest priced, followed by Canadian maple leafs and on from there. The larger the denomination the cheaper it is. If you're buying a quarter ounce or a tenth ounce, you're taking a bath on price. Easy to see on Apmex.
Good luck. I've been selling off all my silver, which is "junk silver" as I realized that inflation alone is making it a bad investment. The fact that it's gone down in number $$ value hurts just a bit more.