Ok, so I have started 3 different consultancies which I sold 2 (failed horrible at the other) and I have run larger groups too. My 2 cents:
1. Do not hire traditional sales staff and base compensation on a commission structure. It is the 100% wrong structure for a consultancy.
2. Do not hire sales staff before you have excess capacity in the form of employees, beside yourself.
3. When you do hire sales staff, do not hire sales in the form of client closers, instead hire lead generation staff that finds clients and passes "hot leads" to the principle for closing.
4. If you need help getting deals moving, you can initially reach out to a friend or others, but very specifically structure it as a referral fee for any deal you can close. e.g. you own the customer, they bring the customer to you, you set the terms, project guidelines and tone for the entire relationship with the customer. Once the deal is closed the referral gets paid a fee (8-15%), usually deferred until the client has made their first payment. So this way they can't bring you someone, then the client closes a deal but never pays you but you still had to pay a referral. Sometimes people balk at this, but to me it is non-negotiable, and the first time you ignore it and pay out a $10k referral for a client that cancels or stiffs you, it will become non-negotiable to you too.
Traditional sales staff is motivated by getting the client through the door and tells them all kinds of wonky things to get that done and get a signature on the dotted line. Then you have to live with that in the deal because the customer will come back and say, well I was told XYZ. Then you are caught between a rock and a hard place, even if the contract doesn't state it, you could still be on the hook if for no other reason then to keep a customer happy. This doesn't happen when the PM or Principle manages the customer because they own the project to completion. Hence, when you get bigger, let the lead generation staff get you the clients to talk to, you or an account/project manager then close the deals.
If you were selling product it would be totally different, but you are selling your and other peoples time which is much harder to do correctly. I have probably made most mistakes possible and paid some heavy prices for them in the past, but using referrals and lead people always worked well.