How hard is it to go to National Guard “Traditional” OCS?

The selection process is relatively the same as Federal OCS, take into consideration that I commissioned in 1985 during the Reagan build up. At that time, the State would solicit all those that met the basic qualification, a degree and a 110+ GT Score to see if you were interested in OCS. We then had to take an aptitude test, and if you scored high enough, the rest of the process much like you have today. You submitted a packet with LOR's from your commanders, then went before a board. Although it was allowed to Commission in the Guard and Reserve with only 90 credit hours, all of the class I commissioned with had 4 year degrees.
The actual schedule for the traditional route varies a bit from state to state, but generally one or two "pre OCS" drills, then an AT period, a year of drill weekends, then a final AT period and commissioning at the end. The first couple of drills tend to be a combination of getting you the requirements and harassment. The harassment will continue throughout the school.
Upside is that you can work civilian job and commission. If you are smart and actually study between drill periods, the academics are not difficult.
The downside is having to psych yourself up once a month to put up with all the BS harassment. I detested my TAC's and still do to this day. I finally just considered them a trial I had to overcome to get what I wanted.
When I attended, most of us already knew what Branch we would commission. If there is one big advantage, it's that you have much more control of your branch. If you are planning to stay in the Guard, I would look at the units in the state. Combat Arms are the biggest branches, just like the regular Army, followed by Engineers. I commissioned Infantry and later branch transferred to the Engineers when I moved to Kentucky.
From that point, the schools move back to Active Army.
The drop out rate in the Traditional OCS is much higher than Federal OCS. IMO, the big reason is that it is hard to maintain a high level of motivation over 14 months.

I graduated from Minnesota Military Academy as an Army Reservist. Granted, it was awhile ago.

For Reservists, we had to meet all commissioning requirements before we were allowed to attend. National Guard Soldiers could work on those requirements while attending OCS.

Academic requirements were the same as Federal OCS. In fact, we took the exact same tests. The benefit to Federal OCS is you get it done all at once. Several people can't take that much time away from other commitments, so the State OCS program works well for that. Many find it difficult to stay motivated and go month after month. We lost over 50% of our initial class.

I would certainly recommend the program.

Traditional OCS will vary from state to state. The benefits of Traditional is the ability to digest the information over the course of a year, rather than drink from a fire hose for the 4 weeks of Phase 2. Phase 1 and 3 are both 2 week trainings that are mainly all field time, while Phase 2 is more classroom and tests. I enjoyed the traditional route, even though I know I could have completed the accelerated just as easy.