If you don’t do created player?

[jellingwood_PSN]

If you are not doing the created player should you sell all equipment and sponsorships?

[Dolenz_PSN]

Sponsorships are only for franchise if I recall.
Equipment can also be used in Road To The Show.

If you have no plan to play either mode then I see no reason not to sell them. Maybe keep some equipment for the cheap 1 or 2 points you can get in the daily quests for exchanging them.