No worries mate.. My advice, totally do it yourself dude! DO IT!.. thoughts on the fly...
I think you'd agree, say work uses it the next 3-5yrs.. think past the PC, in time staff will be walking around with tablets adjusting data.. so build with both in mind (responsive design)... leave the phone out, reduces languages, complications and not really needed for this project... Cool!...
Pro - You know exactly what you want
Con - Instead of starting at ABC, your starting at XYZ
So its going to be a hard road but by no means out of reach..
At the end of the day you're going to have to make a choice.. To take the red pill (php).. or the blue pill (asp)... Google search some "PHP vs ASP" articles to get an idea.. the 2 biggest chess players in the game.. its a 10+ year war...
PHP - Free, therefore endless options, little tricky, 70% of market (estimate)
ASP - Microsoft, very controlled, very easy, little more expensive, 30% (maybe less?)
View YouTube tutorials to see how they both work and the software people are using!...
Will also need to know a little:
A. HTML - Holds things in place
B. CSS - Background colour or image, font size or colour, menu's/nav's etc - makes page pretty
XYZ. PHP & ASP - The brains!
Start with a basic program first week or so (notepad++) free just google.. its notepad with a couple of extra goodies.. eg Folder tree menu to see all your doc's.. when learning is handy to see and help the brain (your's)... preview page in browser option in top menu's, handy.... save pages with ext .html not the default .txt same in notepad if you want...
1.HTML5 (5 is just latest version)
2. CSS/CSS3 (old/new, so till using parts of both)
These 3 work on your PC fine, PHP & ASP online only!!!
So have a play with the other 3 first then look into how to get the "brians" to work on you PC.. starting reading around PHP forums...