The 10-key vault crate is the one to get. Don't bother with the others.

Generally don't bother with buying pilot implants from the store unless (maybe) it is a gold legendary one. Those cost a lot of A-Coins so right now you shouldn't bother if you're f2p. You occasionally may want to buy blueprints but first I think you should take a while to figure out what gear you want.

Definitely don't bother spending A-Coins to reset combat points. A-Coins are for upgrades, blueprints, Epic/Legendary pilots and gold implants. Don't spend them on anything else and hoard them as much as possible.

This game has a strong p2w element but f2p players and low spenders can still make it work. You actually don't want to climb the ranks too fast as you'll get tougher AI and human opponents. Just realized that you will run into a bunch of human opponents that are quickly paying up the ranks and you'll be outgunned. You can learn to be a better player than them, while they are rushing towards the top ranks to get eaten up, so be philosophical about it. Some small spending can be helpful (remember this game doesn't have ads) but I would wait for a while until you understand the game better.

F2p players really have to be careful on what they spend their resources on. Unfortunately it has been years since I started playing this game and they just made some big rebalancing changes so I don't have the best sense of what a begining player should now do. I think it still makes sense to focus on getting 3 mechs but focus on upgrading Panther and Killshot most as these are great mechs at every level of the game.

For other resources, I recommend the YouTubers Scape211 who has lots of great guides and tutorials and GangstaJabs who does great breakdowns of the latest meta so you can understand what gear holds its value long-term. Also you probably can get questions answered faster at the Mech Arena subforum of the War Robots fan forum. Hope that helps some!

https://youtube.com/@scape211

https://youtube.com/@GangsterJabs

https://war-robots-forum.freeforums.net/board/45/mech-arena

I second what S1E1 has said.  

There's 5, 10 or 20 keyvault and 5 is crap, 20 always cheats on you. So just go on 10. Keep the A coins as much as possible. 

If you need to upgrade, then chose 8 level weapons or up to upgrade, "slowly" meaning once per day. b/c you have to spend 2000 C coins daily, and upgrade one per day to hit that quota. Thermal Lance is level 6, and useful for double damage.

There's https://www.reddit.com/r/mecharena/ forum that has discussions on which weapons to choose. Honestly, don't worry about making mistakes or upgrading wrong or stupid stuff. It's just a game. ;-)

On Youtube, you can find scape211, Mayer's Gameplay, Omniverse, and Honor Gaming that has useful contents. 

Add friends with frequent players, and either wait for their invite, or invite them to play Control Point Clash, or 2v2, 5v5, or Tournaments. You earn more points. 

You do NOT have to spend real cash to get better weapons, mechs, or items. You can do so, however, but usually they are expensive; cheap ones are not as good as you expect. I have purchased cheap ones but not very satisfied. My friends have all maxed out specs - I'm pretty sure some of them are Devs or community care team, or just individuals who pays big bucks. But we spend a lot on consols, their games, items, and other games, and apps, so... cheaping out on Plarium isn't that fair neither. LOL. There are people who claimed to have spent over $$$$ on Mech Arena! Wow. Maybe they baught the stocks???!!

There's always great way to enjoy and win a lot in Free-to-Play. Invest in your path, your pilot and matching weapons etc. What mech you want to use the most. Pick and chose implants that synergize the best of your mech and weapons. 

Bots and other powerful players will intimidate you, but don't get triggered; just know what items and skills they use, and counter them next time. 

Learn the rules of the battlefield, hide, sneak out, use element of surprise, etc. Have fun!

if you participate in Tournaments, daily/weekly/monthly or special events... you get rewards faster. 

Join our clan: SpicyKiller [SYK] Clan ID#: 32452

Looking forward to meeting you online!

2 cents from a fellow noobie noob. 

Truly the best advice is to play and have fun without spending $$. I've spent some on a few accounts (my own, my children's accounts) and the more I invest the harder the game becomes + less win ratio. I have a little account that is pure F2P and my win ratio is about 91% and generally I have much more fun due to my opponents not 1 shotting me constantly. 

My kids got me hooked on the game and now they do not play at all. They realize everything is a one-shot kill so they are eliminated very early. Anyways, you want to generally focus on how you play. The most effective playstyle is peek-a-boo (around corners, behind objects, using curved weapons etc).

Stick to your guns and just enjoy the free experience. You won't regret it.