I have a 13.5 EVO too. GSP is great, you just need to be smart about where you place it. Like Rick's Reviews said, an Island is a smart move to keep it from spreading to the main rockwork. I have a small GSP island in my EVO and some growing on the back wall. Since the EVO is so small and space is limited, I do have to occasionally trim the island as the GSP will grow out over the sand towards the main rockwork.
Keeping your lights limited to limit the ugly phase isn't a bad idea. Soft corals, most LPS, and GSP can do fine with lower lights, so dialing in your lights shouldn't be a a limiting factor in adding those corals (in fact, they'll "acclimate" to your lighting during that period too). The ugly phase will come no matter what. Lower lighting might limit the growth, but I wouldn't go crazy trying to remove any of the algae unless it's a real problematic variety. Most of the rest will go away on their own or be held in check as the tank balances out. I also agree that adding some live rock (even just small bits of rubble) can help in the long run by adding biodiversity to the system.