The choice between SH3 and SH5 also depends how meticulous you are, I mean if you want to spend much time to watch series of videos showing you how the modded SH5 interface is working and how to play, then alright go with SH5.
The modded SH3 also needs to get used to but most big mods come with a detailed manual, which isn't true for the modded SH5.
With SH5 TWoS you can play with 'Real Navigation' or without but in both cases the game is generally at very high difficulty when it comes to escape destroyers or your sub resistance when taking damage. Planes are also deadly in TWoS, you aren't going to use your canons very often
I would go with SH3 first, e.g. SH3 +WAC, and then if you want it more realistic, then play SH5 TWoS. In TWoS with the absence of a good manual you are supposed to know everything about how to play, that's rather bad for newcomers.
I have transformed TWoS to suit my needs, but this is not possible with U-Play or Steam version where you can only install TWoS and play it as is. You don't have the freedom like in SH3 or SH4 with mods.
XS