• Chat with the Investor in Hub and ask about an investment - tell him what for.
  
• If he likes your plan, he'll invest some money with you.
  
• Thankfully he is forgetful so each option to ask for money is repeatable every week, 48 hours, or 6 hours depending on the amount.
  
• He will never ask for a return on his investment. If you change your mind, you can back out before selecting how many cats you'd like.

What to do with the money? You've passed your charisma check and got the money so it's up to you. Personally, I'd use the 2k cats to buy the bonewolf and put the 5k and 1k cats toward saving up for the thieves guild payment. Normally I'd never buy a bonedog so early in the game, but, with this one having no death items, there's a decent chance you two might actually make it!