Hello, If we hire employees on contract and in our payroll should we provide benefits or only contribution to pf??

Depends on company policy contract employees are normally paid by invoice not in payroll I would suggest you to do the same and deduct TDS - for consultant you need not contribute to PF

When you say invoice should the person have gst

If the person has his/her service firm which lends contractual employees he can do this in the name of that firm and claim GST however for an individual it is not mandatory for them to have a GST. Also it depends on who the contract is with if you have the contract directly with the employee then you would be paying them consultancy fees in this case TDS needs to be deducted. If the contract is with a firm the fees might have some GST component associated. For individuals it is not mandatory for the invoice to have GST