Hello ndlaw2k, and welcome to the forum,
You absolutely can plan your own European vacation. I've been doing it since before email and the web (Rick used to have a form letter to fax to hotels inquiring about reservations) and it is so much easier now.
My first tip is count nights, not days, and create a spreadsheet or a list with each night and where you are sleeping. This makes sure you are reserving something for every night and have all nights covered. Then you can fill in travel details for the travel days on those days you travel and what you want to see that day. Keep in mind 3 nights somewhere si 2 full days with days of travel either side.
Be careful of European days being marked the reverse of American dates so 15/2/2027 not 2/15/2027. The calendar on the reservation site will act the same but it's something to be careful about. Also be careful with 16:00 being 4:00pm and 6:00pm - it's a mental error that's easy to make if you're not used to military time. Trains run on 24 time not am/pm. Most of the rest of everyday Italy uses 12 hour but trains, museums, and places that hate ambiguity will be on 24 time.
Get guidebooks for the places you want to see. A good guidebook will save you time, money and missing something you really wanted to see but didn't know, or have details. about. Rick has good hotel guidelines and restaurant recommendations. These I lean on the internet more for places to eat and drink as they are constantly updated but having a solid recommendation when you are vacationed out is a great thing. If you use Rick's books read his reviews carefully. One of the things I like about his work is there a lot of subtext embedded in his reviews and observations and if you read him carefully you can learn a lot about a place. Booking.com is great resource for searching but I always then try to book directly with the hotel I've selected if I can. Rome2Rio is a good starting point for general questions "How long does it take to get to Bologna from Florence? How about Milan?" and broad searches but always confirm any information you are counting on with the actual source.
Now the only criticism I'm going to make of your plan is with 11 days you don't have time to do Sicily. Sicily requires two flights and needs at least a week - better two weeks - all by itself. With Florence and Rome you might have time for 1 city in Sicily but the two flights are going to take up way too much time out of a tight schedule. With 11 nights I would pick a 3rd mainland city or add some planned day trips to your two city schedule to see some other cities. Rome, Florence, Venice is classic first Italy trip for a reason, but you don't have to do Venice if you're not interested. (It's on of my favorite cities.)
Set a schedule, break your stay into chunks for easier planning, ask for advice and help on the various pieces put together a plan. In the end there is no way to learn or get better at then to go and do it. There will be issues, probelms and misunderstandings along with amazing moments and revelations. As with anything the more you do it the more you learn and easier it gets, but without a first trip you'll never know.
Happy travels,
=Tod
PS "AI" aggregates (some would say plagiarizes) the combined postings of the internet but it had no actual experience or intention. I will always be more interested in a personal personal experiences when it comes to travel than the average of 1,000 websites, ads and blogs.