Consider how you will use the rig most of the time. Are you just going to the lake or campground for the weekends? Are you going to drive across the country to National Parks? Are you planning to full-time or snowbird?
These are important considerations because of the weight you might need to carry. Slide outs and automatic levelers add considerable weight to the chassis, thereby reducing the amount of people, pets, clothes, food, and water you can carry with you i.e., Occupant and Cargo Carrying Capacity (OCCC). Remember that in RVs, it is not the space you have for stuff, but rather the weight of the stuff that counts. This is not to say that you should avoid these choices, but rather understand that they will effect what you can carry. Further, make sure the rig will be functional and usable with the slides in. Likely, you will spend a lot of time driving, and you can't have the slides out then. Usually, dealers will show the rigs with the slides out demonstrating the available space. Make sure to see them with the slides in as well.
As to your question about leveling, many of use the blocks you can buy at Walmart or Camping World. Many times we don't need to level, but if we do, we use the blocks. Always make sure, no matter how you level, to keep one wheel on the ground.
Good Luck with your search.