7.5g is even a bit small for full boils on 5 gal. You really need to watch them and adjust temperatrues to avoid boil overs, especially on high gravity beers and when adding hops. I have a keggle (15.5g) and it still boils over when I’m not being watchful. I would say that the brewpot is one of your bigger initial expenses so if you’re already going to spend 60 bucks, you may as well spend 100 or 150 to get up into the 10-15 gallon range… ESPECIALLY if you want to do all grain batches in excess of 5 gallons. If you don’t you’re going to end up spending that much later and have 2 pots (not really a problem but still unnecessary).
In terms of the bells and whistles, the valve is a must. You can buy a pot, drill a whole and do a weldless fitting, buy one with a valve on it or whatever but you don’t want to try and lift a full boil pot. 8.3 gal/pound for water x 9lb for a full boil is 72+ pounds plus the weight of the pot and that does’t even account for the fact that wort weighs more than water.
Thermometer is helpful, especially if you’re using it as a HLT, but not necessary in a brew kettle. The sight glass is a total waste, and a pain in the ass to clean. Open the lid and you can see exactly where the water level is. If you’re maniacal about knowing how much water is in there, get a gallon jug, pour a gallon in and make a notch on your mash paddle for each gallon up to the top.