You should only rent a car if you want to see some off-strip sites (Hoover Dam, Valley of Fire, etc)--and honestly usually a first trip there is plenty to see just on the strip (and maybe a day downtown.) In our many trips we have rented a car just a few & only if we are heading of strip for a specific purpose. Plus if you drink, a wise choice. The strip is very walkable.
Do not take the monorail--it is generally inconvenient & overpriced. We tried it when it opened & found we could walk from MGM to Ballys as fast as it took to walk ALLLL the way back to the Monorail, wait for it, then walk all the way back to the strip from the Ballys station. Take the bus. Cheaper & more convenient.
Midstrip is a great location--Mandalay Bay to Encore is about 3 miles. If you stay midstrip, you can go south one day, north another. Easily walkable, or a $10 max cab ride if you decide to cab it back. Ballys, Flamingo, Monte Carlo are the most budgetary closest to midstrip.
I disagree that if all a person wants to do is gamble it doesn't matter where they stay. Most who are coming to Vegas (particularly for the first time) like to gamble but mostly want to see everything--and those casinos have plenty to see. After all our trips we still prefer to stay midstrip. We are also fairly loyal to the casinos that give us comped rooms & we do generally only gamble in those casinos. But we don't like to be stuck at one casino.
One thing about conventions--if it is a very very large one, you will know it as hotel prices will be through the roof. Otherwise, 10000 may sound like a large convention, but honestly there are 125K hotel rooms in Vegas, so it will only affect prices/crowds where/near it is being held.
Again--if you give your travel dates & budget I would be happy to give you more specific suggestions!