How difficult is it to get SMP my sophomore year, and what impact does it have on my ability to compete in ROTC and for commissioning?

Talk to ROTC unit at your school in addition to your future reserve unit about SMP. Some units are supportive, while others find it a burden. The cadre, fellow enlisted soldiers and fellow cadets should have some answers to your question.

By doing ROTC, you get commissioned without OCS. You do have to do ROTC camp in summer between junior and senior year. Side note, basic and ROTC camp are very different. Basic training teaches you how to perform fundamental tasks as soldier while ROTC camp tests you on your ability to be a leader in textbook combat drills alongside garrison life.

As for time, it is ROTC and reserve unit dependent. When I was cadre at University of South Carolina, some ROTC cadets were able to get exemption based on concurrent training (i.e. ROTC FTX counting in place of drill). Some are flexible while others are not. Keep in mind to be physically fit and disciplined within both your reserve unit and ROTC unit. (Both will do sporadic APFT and drug tests)

I'm looking at your question and asking why. Why spend time in a Reserve Component unit while you're in college? I understand if it's about money. You will have to balance many requirements as a college student, ROTC Cadet, and Reserve or Guard enlisted person. I expect you can complete your ROTC program with few problems. ROTC normally has academic classes in the fall and spring semesters and a requirement to attend "summer camp" at some point. It sounds great if your Reserve Component unit will allow you flexibility in attending basic and AIT. Remember that they will issue you orders for this training and they may or may not be as flexible as you might expect. Filling training quotas is important to the unit. As you indicated, you might be the one having to be flexible, like skipping a semester of college to attend your AIT. (Some schools give college credit for some AIT courses. Check with the school after you complete the training.) If you complete an ROTC program, you normally will commission after graduation. The ROTC office will have information about various scholarship and non-scholarship programs and the types of commissions you might receive (reserve or regular). You will have to be honorably discharged from the Reserve Component in order to accept a commission. This should be a formality, but still has to happen (you can't be a Spec4 and an LT at the same time).

If you're a law abiding US Citizen, security investigations are no big deal. For a Secret or TS, you'll have to fill out lots of forms, usually on-line, covering your life for the last 10 years or more. You'll need to enter data on everyplace you lived and every organization you ever worked for. Detailed information on you, your spouse(s), kids, and your parents and in-laws will be required. Overseas travel outside of Government employment (includes military) will be looked at. Associations with foreign nationals will get a close look also. Fill in the forms completely and carefully and keep a copy. At some point an investigator will interview you. Review the forms you completed before the interview so you don't accidently contradict the information on the forms; however, if you discover a mistake, admit it and point it out to the interviewer. Some stuff that is adverse information can slow down and possibly prohibit getting a clearance. Most of it's obvious: bankruptcy, illicit drug use, association with foreign nationals of enemy nations or groups, violation of security laws or rules, felony conviction, DUI, etc. The actual security clearance in granted by a real senior management person, usually a general officer or civilian equivalent. The investigators make recommendations to that person. The senior managers most often go along with the recommendation, but can make exceptions.

Obviously you have to be reserve or national guard. You understand that. Depending on your MOS will decide what clearance you get.

If you enlist before attending college, you’re already qualified to enter SMP if you do ROTC.

What school(s) are you looking at?

Drill is only once a month. AT once you contract, I believe can be waived or RST completed if you go to a summer camp with ROTC depending on your commander.

As for what they look for in a clearance they ask about your history and character. To people you lost as references. Plus your family.