A little bit more on this, in case anyone is interested. I've found a few websites, including some Spanish-language sites which have some good information. The Chilean Navy has a particularly good archive for this era but it does need to be accessed via a wayback machine.
At the beginning of 1836, from what I can work out, the Chilean Navy had three warships (transports excluded) – Aquiles (brigantine, 20 guns), Valparaiso (corvette, 20 guns) and Colo Colo (brigantine, 5 guns).
The Confederation had twelve – Libertad (corvette, 24 guns), Socabaya (corvette, 24 guns), Confederacion (corvette, 22 guns), Monteagudo (frigate, 11 guns*), Santa Cruz (frigate, 20 guns), Arequipeno (brigantine, 6 guns), Fundador (brig, unknown), Junin (brig, unknown), Oebeguso (brigantine, 6 guns), Limena (schooner, unknown), Peruviana (schooner, unknown) and Yanacocha (schooner, unknown).
(*) The Monteagudo was a Spanish frigate captured in the 1820s. It was subsequently used as a transport, which may explain the relatively light armament.
Although not balanced as a starting point, in July 1836 the Confederation lent two ships (Monteagudo and Orbeguso) to Ramon Friere. Friere was the former President of Chile, living in exile in Peru, and the ships were to assist him in a coup attempt. It didn't work and both ships were captured by the Chileans.
The Chileans by this point have 5 warships to the Confederation's 10. Crucially, though, in terms of the most powerful (i.e. 20+ guns) the Confederation have twice as many.
But…
In August 1836 (still before a formal declaration of war) the Spanish officer Victorino Garrido, in Chilean service, entered the harbour of Calloa on a 'goodwill' visit. Goodwill seems to have been in short supply, as during the night he stole away with THREE Confederation ships (the Santa Cruz, Arequipeno and Peruviana). The cheeky chappie then added these to the Chilean navy.
So, by the time war is declared in December, the Chilean Navy has 8 ships (of which 3 mount 20 guns) and the Confederation have 7 (including 3 of 20 guns or more), with a small flotilla of French privateers engaged during the war itself.
That to me looks like a nice balanced starting point for a small campaign.
Nick