If they don't have accounts with their suppliers or a credit card that can handle the payment I'll want to know why that is but in some cases I'll buy the materials and make sure they get to the job site.  

Check with small local suppliers and see what deals you can get, and what warranties they have. 

This goes for suppliers snd subs as well, but that is another story...

These are two very well known suppliers, with multiple locations throughout KY and OH, I used when I had an HVAC company in Louisville.

The unit cost are set from the suppliers.  

(sorry for the pun) on your job-site.It's the same game as in the states, but played in the context of a different culture... which calls for different strategies in dealing with supplier relationships etc...

I've a supplier on the 500 block of Washington St.

Even after work has commenced, this was debated between the architect, electrician, and supplier, so how would I know that off the top of my head going into this?

I remember you saying that you were doing a lot of good reading and it's a good one to add to the list.On top of starting to get pricing for local estimates, you can start using your visits to properties to make room by room checklists so when you walk a property you'll get better and better at notation items to help with your estimating and the creation of your scope of work.You might want to start checking out suppliers - don't forget to familiarize yourself with some of the used building suppliers in your area - Restore, etc.  

Hains Criss Cross is another supplier of data and the BWI Meetup offers.