It's more ideal to have good quality in place that needs bedding in than it does to have way lower quality (and quantity) than what is needed.
Signing a right back is needed as long as Rafael isn't trusted and can't stay out of the physio room. Valencia is neither a right-back nor a winger anymore.
We might keep Valdes, meaning that he has been training with the players for quite some time and he has played under Van Gaal before, not a big change except for the very big drop in quality.
We need a CB, we have 2 injury-prone first-third choices whom neither are top-quality (yet), and behind them we have Blackett who is far from ready for even a backup spot, McNair who is a good backup and Evans who is a crawling dissaster. We definitely need a CB of top quality.
We currently have an aging Carrick who is also gotten more injuries, he is a key-player who will need replacing, either by a backup to Blind or a top-quality player. Having only one player to fill in for Carrick here is a issue. (Personally I don't think we need 2 midfielders, we need 1 and could get away with bedding in Pereira)
Depay is already signed, and though it on paper might not have been needed, he is a top talent and with Young aging, Di Maria not settling in (or deemed a winger for LvG yet) and Valencia pretending to be a right-back we only have Januzaj behind them who is more miss than hit.
With the system more set, Depay offering goals from the left, less injury issues and a proper defense and backup for Carrick, our attacking lineup will be fine without a striker, even if it ends up with us having Rooney, Chicharito and Keane as our alternatives.
Of course I'd love to add another striker, but failing to do so won't be a big issue if we can get a better platform for them to play on.
I get that you are worried about the amount of players that are potentially coming in, but the issue would be much bigger if we had to rely on a back-line of Blind, Blackett, Evans and Valencia, with a midfield where Herrera is our best defensive-contributor (and creator).