As a general rule I'd agree that's probably OK, but like most things, there's exceptions. Start throwing a mix of new and used equipment into the mix and it doesn't necessarily stack up. You'd get a used component with superior performance, relative to the new components and that might throw out the balance. Also there are going to be some items that punch well above their weight, sound-for-pound and again, you may find the resulting system unbalanced (or at least underperforming vs potential).
Also, without wishing to stir up that hornet's nest YET AGAIN on cables, stands, power, foo etc, on a system around the £1200 price point I'd say stick with basic and cheap. No point splashing out hundreds on fancy interconnects at that level. You can always play around at a later date if and when budgets allow. There's always stuff going on the Wam at decent prices, or someone like Mark Grant if you want new and good, but not pricey I/Cs and speaker cable. Stick with the standard power cables to begin with. Don't worry about outboard PSUs. Canny purchasing of accessories takes the sting out of things and still allows the lion's share of the budget to go where it should, i.e. the main components