Cashflow is gonna be a problem until you get up and running with more work more often. Someone else here said don't be affraid to ask for a small deposite upfront and they are right too, you should be asking that. You will get times like this job where it's a bit more difficult. Your very unlikely to get credit from any shops too, it's important that you tell your customer that if you are supplying the materials that you will need that re-funded the day you start the job, most are fine with this as they can see what there money is being spent on.
There were so many times where i would borrow a score from a pal just to buy one bag of addy, turn up on the job and do a bit of work so they can see what your about (and see all your tools on-site) then i would have a friendly chat with them and make up some reason as to why i didn't pick up all there materials (you could say that you had to go help someone out on their job late the night before and you didn't have time to pick them up, anything, just make it sound like your the dogs) Then tell them that you left your bank card at home and is there any chance you could take some money off the job rather than having to drive all the way home (loosing time off their job). I always used to say that it weren't a problem if they didn't want to do it (but cos you have now done a days graft and all your tools are there they are 9 times out of 10 fine with this) or you could just be completely honest with them and tell them your skint, weigh it up withe each customer.
I know it don't sound to professional like this but you are gonna have to do whatever it takes and at times swallow your pride just to get a job done............. Remember, the customer is human and they too at some point in their life would have forgottoen their keys or wallet or something else and they know you are know different, as long as you word it right and are polite and don't put pressure on them they should be fine (and they don't know your skint.
Also start putting into your quotes now that you wont ask for FULL payment until the job is complete and they are happy with your job but you do ask for a small amount after your first days work (say £100 - £200) to cover your material costs (remember they dont know your skint so they aint standing there thinking you need the money so you can get screwed) and besides this is perfectly normal practice in the building game......... When you get bigger and cashflow is not a problem then i personally never ask for anything but we all have our different ways and you'll find what best suits you too.
As for the socket issue on your job i would just tile it as normal and if it looks too sore i would Silicon or i would grind off any large lumps that are making it stick out so it sits a bit more flush with the tiles, each to their own mate.... horses for courses and all that. good luck