You got yourself a decent detector.
By all means, if you can, if you have a place you can start a little test garden then by all means do it.
Now that it is winter (don't know what part of the country you live in) its a good time to start one.
By spring the metals will have enteracted with the soil to such an extent that when you test, you will have a better more accurate depth reading. Most people I have talked too say that its more difficult to find your coin in a freshly dug hole. I suppose that depends on how deep you dig those test holes. Even if its a 4inch hole you shuld be able to detect your coin regardless.
Like it was said by another member here, yes your machine will pick up gold nuggets, but the Ace 250 was not intended as a nugget hunting machine. You probably WILL find some nuggets. In fact recently the Garrett News Letter ( you can contanct Garrett and subscribe to it...I believe its free ) had a short piece about an Ace 250 owner who found a nice sized gold nugget in ALaska. Thats amazing considering how mereralized the soil is there.
After you have been MDing awhile and you decide you really like the hobby, you might want to invest in an all around MD machine like an MXT or one of the MineLabs....both excellent gold machines that not only does coin/jewelry and relic hunting but prospecting as well. Whites has a detecated GMT Goldmaster that is strickly a prospecting machine, but thats probably down the road for you I think? Fishers has some good gold machines too.
You'll have a lot of fun with the Ace 250. There are lots of MD forums to join as well. The old timers will be loads of help to you. Ask all the questions you want.
Happy HUnting.
Regards
Robert R