Hi!
I also recently went through DCF at the London Embassy earlier this year and this was our timeline:
13 Jan – Contacted immigration lawyer
16 Jan – Lawyer submitted the DCF request to the Embassy
17 Jan – Embassy replied, offered an appointment
29 Jan – US citizen spouse went to the Embassy to file the I-130
7 Feb – Received I-130 approval letter and case number
12 Feb – Booked interview for 25 March
13 Feb – Submitted DS-260
11 Mar – Medical exam in the morning, then document check at the Embassy (the document check is a new step that started in Feb 2025)
25 Mar – Visa interview – approved!
To answer your other questions - our I-130 approval came as a physical letter in the post. We did use a lawyer, but this was mostly for reassurance, I wouldn’t say it was necessary. We had a very tight timeline for moving so didn’t want to leave anything up to chance. I think the thing the lawyer helped with the most was writing the initial DCF request. All the subsequent steps of the process came with clear instructions from the Embassy so I don't think the lawyer made made too much of a material difference after that - although it was nice that they put together all the supporting evidence and paperwork!