You will need to determine the total wattage required for the lighting fixtures, in this case 300W for spotlights and 450W for the well lights. You will see I used 75W instead of 50W to determine the wattage based on worst case scenario. You may find 50W doesn't provide enough lighting for your taste.
Next you need to determine if the manufacturer offers transformers that will provide enough power. Most have a number of different wattages you can order to meet your specific needs. Inyour case it might be cheaper to buy one 300W xfmr rather than two 140W xfmr.
You also need to find out if the manufacturer provides hard-wired or plug-in, and which type suits your need. If you go plug-in, you need to provide a receptacle with a GFCI, weatherproof receptacle and a while-in-use cover, near the location of the xfmrs. Please note weatherproof is NOT the same as a while-in-use cover.
You will need to install and located the xfmr(s) per the manufacturer's reccomendations. If you install inside, you will need to run the extra length of low-voltage wire from the xfmr(s) to the lighting fixtures.
If you want to install a photocell, you will need to place the cell up high enough and oriented the right direction on the exterior of your house. You will also need to run a power feed from the panel to the cell, and than from the cell to the xfmr(s) OR you can tap into an existing photocell.