Gday,
Being tall has it's ups and downs. It's easy to stand out in a crowd.
The main thing to do is make sure whatever costume you do, that you're proportionate.
This means spending a little bit of extra time on your armour, perfecting the spacing, trimming (if you go kit form) and fit.
Alternatively, if you're good with a sewing machine, an Imperial Officer is a great way to jump on board for mininum outlay to give yourself a bit of time to work on that "special" creation.
Sitting, running, kneeling may not be an option to different costumes - so you may also like to see a few builds at an AP or 2.
I'd encourage you to come along to a troop, see a few different costumes and armour makers products before making any big dollar decisions.
I think you're in the right place to live out your childhood dreams.
All the best,
Cutter