Hi there,
I will represent the advocate on the other shoulder.
Having looked at your installation, I think you have done a pukka job.
From what you have mentioned, the customer is not looking for the most
complicated setup. It's a great first time project to get the ball rolling.
To steer clear of most of the suggestions that the pro's have mentioned I would suggest the following;
1. Specify components that you know will work well together and are reliable. By the sound of things, you are not trying to sell on the kit to him for a profit so specify it, let him buy the kit himself (perhaps advise on locations to buy from) and help by making sure he understands the warranties on the items.
This way, if something breaks down during the warranty period, he can arrange the replacement and he can expect to pay you for your time to swap it out / re-install it.
2. On the IR dimmers, once again specify a decent make that will work well with the Logitech remote and tell him that a local electrician will need to fit it if you are not one yourself. This need not be an expensive exercise assuming that there are only one / two switches for the lounge.
Getting into the game of doing it for others and earning out of it is never easy, I have had to go through this for the last 18 months and am only now starting to get the costing right with regards to labour. Things always take longer, especially on entire home refurbishment jobs.
The one good thing is at least it's only next door and not an hour's drive away so it's a very good first time job.
We usually have a sit down to discuss exactly what the customer wants out of the system (which it sounds like you have done), then go back with drawings of the rooms, product spec sheets, samples (printed off illustrations may do in your case) and a quotation. We go over the solution and make sure we have covered everything. At this stage, it's worth ironing out the final details i.e. speaker positions, heights, finishes etc.
On your quotation, break each element down and put a realistic amount of time in hours to each task. Don't forget the planning / design time.
We build in two contingencies, both of 15% of the entire amount that you believe it will take. The first will be for any issues that WILL arise with getting the system installed & configured to their liking and the second for the inevitable return visits to show them how to do things once you have handed it all over.
30% overall may sound a lot but to date, we have always used this up in one way or another. Up to you I guess as it's a smaller first time / favour / cash type job.
Once costs are agreed, meet with any third parties involved (Electricians, builders, decorators) onsite to agree positions and timescales etc.
Ideally with the customer present. If you are going down the route of others for chasing and electrics, make the customer aware of this at the quotation stage. Set realistic timescales between the chasing, your first fix and the plastering, especially if you work full time elsewhere and are going to be doing this evenings / weekends. It may be tricky expecting the customers lounge to be like this for any prolonged period so a day off your real job after the chasing day might be prudent to get all cabling in. Then the plastering / decoration can be completed in your absence.
The rest is pretty straight forward really - you have the aptitude to do the actual installation, just remember, people are perfectionists when it comes to finishes in their own homes, the smallest details and flaws WILL be picked up on so get it right before any snagging!!
Good luck and post the results!!