You picked what I personally feel is the hardest of the Hunter types to play... Both HUcast and HUcaseal have traps to help them out, which is offset by having no Tech usage; and HUnewearl is notably better with Techs, but lacks HP and Defense. The HUmar isn't exactly
bad at anything, it just doesn't
excel at anything, either; the classic, "Jack of all trades, master of none" kind of class- still a totally viable choice, mind you; he just requires a little more skill to master. Far from the hardest class to learn, though.
TL;DR: That's rough, buddy, but we've all been there and it gets better eventually.
All that said, some actual advice for your problems...
A lot of high-level players really like to help us newbies... Just make an open room named "Newb Grind" on the main ship and block, watch how fast someone pops in to help you out!
If you ask around you can pretty easily find free non-rare armor with 4 slots; once you're playing up into ULT difficulty they spawn in the shops pretty regularly. More than a few people are willing to give you some random low rares to boost you along, too- stuff like God/Body that, while not particularly valuable in the trade markets, would be a definite boost to someone grinding away in Hard and VHard.
Peruse the drop charts for your section ID and find a place to do your solo level grinding that has a chance to drop something useful- especially trade fodder. Making your grind time double as item farming can be very useful not only in helping you get your desired gear (either from drops or trading) but it'll probably force you a little outside your comfort zone; the best drops rarely seem to be in your favorite areas to play, so you have to bring your skills for those enemies up, too.
Rummage around in the boxes you find in Mines until you find a couple spare baby Mags. You're liable to mess up building your first couple unless you're either meticulously following a guide or are just really lucky. Once you've got a few, though, and feel you've got raising them well in hand, feel free to build two or even three to switch between the same way you'd switch weapons. Building a POW-focused mag for maximum stab power and a different one with high DEX to use with guns is totally fine. You probably won't want a MIND mag, though; you can only learn Techs up to level 15, you should be able to reach the MST needed easily enough.