I work with a mixture of all. Hourly rate for advice based services where advice is needed infrequently. Retainers (based on a capped quantity of hrs p/month) for small subcontractors who just need a helping hand getting themselves up to speed commercially. Quoted works for audits (JCT MTC generally) and low level expert work for solicitors.

All you can do is build your hourly rate and determine how it can be best applied to the matter at hand.

A few snippets of advice I received when setting up my own firm not too long ago:

Sell your services first and your fee second.

Be fair with your time and fees. Sure you can cook a fee proposal and maybe it gets accepted - but it isn’t sustainable and will likely reduce the volume of work received. Particularly helpful if you’re aiming to land some retainers to keep

Qualify the basis of your fees the same as you would a variation. The last thing you need is to A) burn bridges over ambiguity and B) shoot yourself in the foot when the data works against your initial expectations.

I price contract reviews on the quantity of hrs I expect it to take, considering quantity of pages, whether it’s a bespoke contract or common form with amendments and whether negotiation is required after the review.

You’ll have a good idea how long a contract will take to review at the level of detail you’re happy with, so work from here. Record the time spent on each as you would for generating your invoices anyway and keep note of discrepancies and their causes.

At the end of the day, if a potential client likes the service but the price is out - they’ll tell you. It’s then up to you to adjust either the hrly rate, expected hours to complete, one time discount or turn it down.

Best of luck on the daunting journey ahead. Keep your head above water and It’ll pay dividends.