My group and I are beginning a new campaign with Legacy of Fire, but unfortunately my DM wants to stick with it's 3.5 format. It's been awhile since I've had to retro think how to build a 3.5 Cleric.
We are starting at 5th level with the House of the Beast chapter of the AP. I've been banging my head against my keyboard all day and here's what I've come up with so far.

Tamarantha
Female Aasimar, lesser
Cleric of Sarenrae/5

Stats (28 point buy)
Str: 14
Dex: 12
Con: 14
Int: 10
Wis: 16 (14+2)
Cha: 14 (12+2)

Glory and Sun domains.

...and that's about it. I'm stumped on what feats to take and what PrC I want to take. Any advice/help would be appreciated.

First question for a 3.5 game...what sources are allowed? A core rules only campaign is very different to an 'everything is allowed' campaign. Though the lesser Aasimar is outside of Core Rules already.

Second question, what sort of cleric do you want to be?

Question #1: Everything goes, with the exception of Eberron. Mostly Core plus Completes, and Forgotten Realms.

Question #2: Given the other classes* I'll be Primary healer, plus Buffer, with a little third string Melee thrown in.
*Fighter/rogue, Fighter, Druid, Wizard/sorcerer.

*Unfortunately?

Conversion comes easy to some, but for other DM's, trying to convert 3.5 adventures to PF can be a serious chore. I don't blame your DM one bit.

To boost healing there is a feat in The Compleet Divine that gives an extra couple of points of healing based on the spell level. I believe The Complete Champion has a reserve feat that let you heal people over time up to half their hit points as long as you have a healing spell memorized. From a buffing stand point I always like the Extend Spell metamagic feat and if combined with Divine Metamagic (Complete Divine) and Extra Turning, you can really get several fights out of buffs.

If you don't plan on fighting much at all, using the Cloistered CLeric alternate class option from Unearthed Arcana, get you more skill points and the knowledge domain which gives access to all knowledge skills.

Since she's going to be, at best, a tertiary melee combatant I've rearranged some of her stats to reflect this.

Tamarantha
Female Aasimar, lesser* (Humanoid (Planetouched))
Cleric of Sarenrae/5
Domains: Glory & Sun

Strength: 12
Dexterity: 10
Constitution: 12
Intelligence: 14
Wisdom: 17 (14+2+1)
Charisma: 14 (12+2)

*+2 Wis, + 2 Cha
Daylight 1/day (CL: 5)
Resistance 5 Acid/cold/electricity
+2 Racial bonus to Spot/Listen

I've decided to go with at least Extend spell as one of my feats. I was thinking about DMM as another possibility but once it's chosen am I stuck with that metamagic feat or can I change my designated feat if I decide to go with the Persistent spell cheese later?

I've decided to go with at least Extend spell as one of my feats. I was thinking about DMM as another possibility but once it's chosen am I stuck with that metamagic feat or can I change my designated feat if I decide to go with the Persistent spell cheese later?

I think you're stuck with it for a specific feat.

Since she's going to be, at best, a tertiary melee combatant I've rearranged some of her stats to reflect this.

Tamarantha
Female Aasimar, lesser* (Humanoid (Planetouched))
Cleric of Sarenrae/5
Domains: Glory & Sun

Strength: 12
Dexterity: 10
Constitution: 12
Intelligence: 14
Wisdom: 17 (14+2+1)
Charisma: 14 (12+2)

*+2 Wis, + 2 Cha
Daylight 1/day (CL: 5)
Resistance 5 Acid/cold/electricity
+2 Racial bonus to Spot/Listen

I've decided to go with at least Extend spell as one of my feats. I was thinking about DMM as another possibility but once it's chosen am I stuck with that metamagic feat or can I change my designated feat if I decide to go with the Persistent spell cheese later?

I'm not familiar with a lesser aasimar in 3.5. Is that something your DM is allowing you to bring over from Pathfinder? Or is that a lesser planetouched template from Player's Guide to Faerun applied to an aasimar?

In general if you choose Divine Metamagic you're stuck with applying it to the metamagic feat to which you originally applied it. PHB II does, however, have some retraining rules that your DM might allow. Even if the DM does allow it, the retrained feat must be one that you could have taken at the level you took the original feat. So if you didn't have Persistent Spell at the level you took Divine Metamagic (Extend Spell), you wouldn't be able to retrain from Divine Metamagic (Extend Spell) to Divine Metamagic (Persistent Spell). If you waited and took Persistent Spell before Divine Metamagic (Extend Spell, you'd be able to retrain, but then you'd be stuck with Persistent Spell for a while without being able to use it.