You mention that you fly several LH flights in J, any one of those flights will give you more than the 5200 missing level miles, and since I'm assuming you also need a segment UK-CDG/AMS, you are looking at 10K+ miles for a r/t, PE flights with AF will also cover that, a UK-CDG-CAI-CDG-UK in PE should give you between 5800-6800 level miles.
The earnonline shopping miles do take time to show up, usually around the maximum possible time (I think it is 120 working days) and you only get miles for the price excluding VAT and possibly also excluding delivery, it's not the most reliable website but you have nothing to lose.
Best usage of miles is probably promo award, especially some can be nice at 50% off, DOD upgrades or upgrading tickets that someone else paid for and are relatively in a high booking class.