Hitchlock and wheelclamps canbe split into 2 main types lighter/quick fitting types or heavier duty ones.
I had an old bulldog style clamp. It was like assembling a meccano set made from iron girders.
Every part was substantial and damn heavy.
Most of the stuff is down to personal preference. One person may rave about something where another will hate it with a passion.
With the leisure battery make sure you charge it monthly with a decent car charger. The vans charger wont 100% charge it. They only keep them at a floating charge to prevent the battery gassing.
Regarding the wheel lock I always use an SAS wheel clamp as it's light, easy to store and is a listed security device with my caravan insurance. However, it depends on whether you have steel wheels or alloy wheels on the caravan as there are two types of clamp. Alloy wheel bolts are recessed whereas the steel wheel bolts are not so if you do opt for this device then make sure it's for the type of wheels on your caravan. Caravan manufacturers changed from steel wheel to alloy round about the year 2000 onwards.
Regarding the hitch lock, there are several types on the market but make sure you buy one that covers the two bolts that secures the stabiliser to the 'A' frame. If you don't then any potential thief can just undo the two bolts and interchange with an independent hitch and tow it away thus the loss of your caravan.
The link below shows the various security products including the hitch lock for the AL-KO 3004 stabiliser. Once you know what product you require you can then search for second hand equipment but make sure that you have ALL the keys with any type of security lock.
Regarding towing mirrors, the best on the market and always gets voted best on this forum is the Grand Aero mirrors by Milenco. Easy to fit, clear rear vision and most important is they don't vibrate like some other brands do.
Below is another highly recommended company that also manufacture security devices as well as towing mirrors.
Different categories are in the link.
As you have just purchased your first caravan you may find lots of questions in the near future. Much of my knowledge was gained from reading the Caravan Handbook by John Wickersham as it explains just about everything you need to know about caravanning and as you are newbies you may find it it extremely useful.