I think this might say it all..."its also my first time weathering (and building) a vessel in a long time, so Im learning something new every day!"
I for one think that this being your first model in a while and your first attempt at weathering, you nailed it. I think just about everyone of the guys here on MSW will agree with me when I say that no one learns this stuff overnight. The best part of your statement is the "I'm learning something new everyday"! It take practice and many models to get to a level in the hobby "that you are happy with"! Yes, British ships are notoriously clean (for the most part...anyone who ever served on one would tell you they do get dirty)but you are after learning the skills of weathering a well as working on perfecting the construction part. Each model will bring you that much closer.
So, in a completely helpful constructive manner, when it comes to construction, it is always a help to build in large sub assemblies when you can; i.e. hull, main deck, superstructures, rather than work from the hull up putting all of the pieces together and then paint. With some ships, this is not always possible, but it ensure parts fits cleanly before assembly and that things like painting and some weathering will be easier for you. "Dry-fitting" is another valuable point. Take these sub assemblies and dry fit them to make sure they sit well with corresponding parts. Such is the case with the forward deck on your destroyer. There is a small gap along the bow where it looks as if the deck is risen above the hull leaving a gap. Without the main superstructure parts installed, this is simple to correct. Probably most of this is due to the parts themselves...you mentioned this having fit issues. Somethings can and will be out of out control sometimes...LOL
As for weathering, go nuts! LOL The only way to pick it up is to do it. I use old models as test beds for trying new things out. Slap a coat of paint on them and just try stuff. More often than not, a simple filter, which is basically a thinned down is a great place to start the weathering process. This will make details pop and give you a good idea of the areas you want to add more too. Weathering is something that is done in layers. With ships, or anything else for that matter, there is a balance between weathering and creating an abandoned vehicle or ghost ship...lol! Some areas, no matter how proficient the navy is, will always have some wear and tear...like around the hawse
pipes. There will always be some sort of streaking and rust in these areas due to use.
In the end, you did a fine job my friend! Keep going....keep learning and above all, keep having fun!!