Yes, you will not be able to place things from EPS that you didn't include using the basegame starter, but it's better than having random strays appear or freezing sims. Fencing in the lot seems to help - perhaps the basegame starter is also what you'll want to use.
PETS also can cause problems with strays appearing. Unless you like simsicles, you'll need to use the BaseGameStarter. You must use Numenor's BaseGameStarter or the Any Game Starter to create your custom CAS lot without Seasons!! Custom CAS lots created in Seasons will cause all sims made within your new CAS screen to freeze to death. To view it, we strongly suggest to download the Foxisoft PFD Viewer: it's free and small, less than 1Mb! If you have the Seasons Expansion: This tutorial is also provided in PDF format. This tute is also hosted at The Sublime Sims Forum/. I've broken it up to make the tutorial as easy as possible for you guys. At the suggestion of the lovely and kind Tiggerypum, I'm posting my CAS modification tute.