When I ran my pure Summoner playthrough from 1.2.4, my rules were:
1. Under no circumstances could I deliberately attack an enemy with a useable weapon that did not deal Summon damage on its tool tip.
2. Accidentally hitting enemies with tools while mining was acceptable, but could not be used with intent.
3. Traps and other arena hazards were acceptable.
4. Accessories which dealt reactive damage were acceptable (Spore Sac, being passive, would work under this policy though; Shield of Cthulhu would not, as it is an active use item)
5. Player starts with a Slime Staff due to general inaccessibility. I wanted the playthrough to be pure Summon from the start, and with my limitations, I didn't see a realistic way of legitimately farming for the incredibly rare Slime Staff.
Combat was primarily focused on evasion and assisting my minion's AI get into range, while recasting Turret Summons from time to time. Some of the bigger challenges were Eye of Cthulhu, Queen Bee (had to constantly resummon my Slime on top of them to hurt them while they flew), Wall of Flesh and Duke Fishron.