Just taking a quick look in the fuse box would tell you if you have beg enough service out there to begin with but with all the things you have described and recent work I would say that you are going to be more than alright. Like Hgdehs stated plug in, I like to use a radio turned up loud so I can hear it from the box, and turn all of them off. Then flip each one until you find the one which makes a crap load of noise
Rinse and repeat for each circuit.
If there is a dryer and it is electric not natural gas or propane then it prob runs on 220v and should be on a 30 amp breaker or larger. I don't run that large a lamp but you should be able to run two 1000w off of it accorrding to Isthis2012.
If you are lucky enough to have the dryer outlet you could use a product such as this
http://www.growwurks.com/30-amp-timer-box.aspx
or like it as there are tons of similar products.
Hope to help shed some light on your garden