To get EP5.3 with the specs you want (ep5 armors, ep3 maps and skills), I would recommend to use EP4.5 Server files (Shaiya Omega files;
[Only registered and activated users can see links. Click Here To Register...]) and Ariez' EP4.5 Client that you can find here on the Forums and just manually add the EP5 Armors and Weapons to the EP4.5 Client (using LPHs Shaiya Data File Tool) and update the Database.
All steps are explained here on the Forums so just use the Forum Search a bit to find what you need.
Yes, it wont just include EP3 Maps, but thats probably the closest you can go, or use the Stoneage Shaiya Lite files to get a EP3 Server, which I dont know if its working properly, but I hve confidence in Omegas files since I used them for every of my Projects so far and everything is working properly.