What schools should a new National Guard soldier seek to attend?

I would ask your unit what do they need. Most units have positions or training opportunities that are unique to that unit. I see that you are in the NCNG. I was there for about 10 years. I was able to get a few schools knocked out before I came back to the Regular Army. I was infantry so the schools I went to wouldn't be of much help. I would focus on signal certifications. I would also use your TA for college. The smarter you are the more lethal you are. College will aid with that. I finished my college in the guard and commissioned.

I'm sure you've figured out that every Signal Support Systems 25U Soldier is considered to be a jack-of-all-trades so your interest in schools should train you to become proficient in all ground tactical communication systems. Look for CompTia A+/N+/S+, (even CISSP) certification opportunities; besides on-line, Fort Liberty, NC (and most large Army bases) has a Signal University and they train/cert Security+, Network+, A+, CISSP right there at no cost (almost always) except for any TDY expense your unit would cover if you have to travel. Your unit can help get you a validated seat if allowed. Fort Eisenhower also has mobile training teams (MTTs) that travel around at the request of units--inquire about their MTT schedule and what training they are conducting. Any training you can get on JCR and JBC-P would be good too, espc, maintenance and adv operation procedures.

SPC (Join to see), log into Army Career Tracker (ACT) and look at your Individual Development Plan (IDP). You probably don't have one yet, but there is a button for CMF Map that shows you all the ATRRS and self development schools that the Army thinks you should pursue for professional development in your MOS. These courses are either ADT or EBDL, so you get compensated for completion (if you have the memos and such ahead of time).

I took a look for you and in brief:
CompTIA Network+
CompTIA Security+
Signal Digital Master Gunner
Management Client Course
Joint C4 Planner Course
SEJPME I and II
Finish your degree! (B.S. in something relevant)

What may help:
Cisco Certified Entry Networking Technician
Instructor Course (CFD-IC)
Master Fitness Trainer

If you are in turbo mode wanting to rack and stack as many courses as you can complete so you can focus on leader development from SGT to SFC, I would recommend knocking out the technical stuff and Master Fitness Trainer (strive for 540+ on your ACFT always). Go up for every Soldier of the Quarter or Year and Best Warrior Boards with the goal to win. Your certifications are going to be the big one on the SGT board. Once you make SGT, look for an instructor unit and get CFDIC knocked out. Stay for about 3 years and grab a Senior Instructor Badge before heading back to a BN or BDE S4 shop. There you would seek out everything else: Signal Digital Master Gunner, Management Client Course, Joint C4 Planner Course, SEJPME I and II.

The Hoah stuff helps (Airborne, Air Assault, etc), but if that is all you have, it will only take you so far if you also are not technically proficient.

Do not homestead. You will be a cage monkey for 10 years, counting handsets and batteries.