Hi, Kent. When you say "you bought this EFB", do you mean you bought an 740 or other iFly hardware device? (I'm guessing you meant a 740, because if you were running it on an Android tablet or iPad, the software itself is free, and you only pay for the data subscription, which you say you have not yet purchased.)
Re: airport diagrams, the setting you're looking for is Menu > Setup > Map Settings > Enable AutoTaxi. This will automatically overlay an airport diagram onto the moving map and zoom in on it (so you can see your georeferenced location on the diagram as you taxi) when iFly identifies your GPS location as being at an airport and your speed as being below flight speed (which I think by default is 70 kts, but maybe someone else can confirm).
Re: Data install. I don't have a 740 so I'm not sure if the data download is different from the way it works on a tablet device, so I can't answer with 100% certainty. But if the way you're doing it is the same as my tablet (there's a graphical representation the US, and you touch the states you want to download data for, and you use the "Advanced Options" button to pick the types of data you want), then I *think* that when it comes time to update, if's only going to look at what boxes are currently checked, and it's going to update those data for all states you have selected. So, I don't think it's going to preserve the "hybrid" data download you manually achieved.
That said, if you're using an iFly device like the 740, then there is no reason to be concered about storage space. The SD cards that come with the iFly devices are sized to hold the entire data set for the whole US with plenty of room to spare. Unless you have tight limits on your internet data plan, or you have a slow connection and are trying to shave the size of the dataset to save download time, there's no real reason to try to micromanage the data downloads. Just select the states you want, and if you get a few extra maps or charts or whatever for some states that you don't expect to use, there's no real harm done. The interface was designed for a compromise between simplicity and detailed selection control.
Still, if you're using a 740 and you still really *do* want to micromanage your data install, there is another way to do it (as long as you have a Windows computer and a way to read/write to SD cards with it): Download and install the "iFly Connect" software from here: http://www.iflygps.com/UPDATES/Download-iFly-Connect . Pull the SD card our of your 740 and insert it into your Windows machine, then launch iFly Connect. Inside that tool, you'll be able to select the specific data you want to download, and once you've made your selection, you can save that selection. Subsequently, any time you run iFly Connect, it will scan the list of selected products for newer versions than what's on your SD card, and update accordingly.