One of the advantages of the summoner class is that it is powerful enough to give you the freedom to take whatever concept you feel like and build it.
One of the disadvantages of the summoner class is that if you set out to optimise it, you'll completely break your character.
The concept you've proposed is sound, will work, and will be more than viable enough to handle what most scenarios will throw at it.
I would suggest: flavour appropriate small race (consider gnome, perhaps halfling): it would be difficult to justify a wayang coming from Lastwall (which prohibits you from taking Wheeling Charge).
Start with 14 str (after mods), and 14 con. Distribute the other stats as you see fit: halfling and gnome both get racial bonuses to Charisma, and even 15 is enough for a character like yours.
Heirloom weapon and Armor Expert as traits (you don't want to take armour check penalty on ride).
If you pour your feats into the mounted combat line, you'll have Spirited Charge by 5th.
You'll be stuck with light armour, so consider Mithril Breastplate (armour check penalty is zero with Armor Expert, so no nonproficiency penalty), or Elven Chain.