Theres been some issues with Windows Update with Windows 7 clean installs for the last few months... You can use the WSUS Offline Update to patch Windows 7, after that Windows Update will work. [URL] However since your plan is to make your system a Windows 10 Pro Device. You are better to just download a Windows 10 TH2 .iso and clean install directly with your Windows 7 Ultimate Product Key: [URL] [URL] 
Inspiron 1720, Win7 Ultimate x64 Did a clean install today on a separate partition. Did not delete existing installation of same OS using the same key. The new install won't download the updates.C:\ shows numerous Windows.old files. Anything jump out at anyone or is this Win10 being Win10 ? PS Would changing this to Win7 Professional help the situation ?  I should add this is a retail SP1 slipstreamed version. As well I was able to get IE 11 installed without issue. 
Can't get Windows updates after a clean install.