OP, what case size do you have? Sometimes a "psu ( current 180w)" system is small form factor (or slim or ...) and the only size card that will fit is a low profile card and the only PSUs that will fit are not standard ATX PSUs.
OP, you specified no PCIe x16 gen2 or gen3.... you know that a gen 1 slot works fine with gen 2 and gen 3 cards.... So if the reason for spending the money is to hook up video then just drop in a new PSU and the card of your choice.
IF you buy CPU, PSU, Graphics, etc then consider also spending another $50 on a case. That will make the install a bit easier. The leads from the case will be labled, their will be mounting hardware that fits the new MB, etc. Another way to say this, build a new PC then transfer over your disk drives and maybe memory.
Note that your copy of windows will work fine on the new MB, however your prebuilt manufacturer's recovery partition will not work any longer (they are tied to the vendor's MB) so figure out a backup strategy. Something like an external USB disk with a cloned image of your disk drive.