The Lowe 1648 I had worked out well when I fished solo or had a buddy in there. With 3 people it would be rather crowded. Being 16' it isn't going to be as stable as the 17' or larger boats, but it wasn't bad at all. As far as big enough you can fill it up rather quickly. I would only load the gear for what I was targeting that day. Two people with each's own tackle/rods and cooler would have the boat full quickly. Solo trips it wasn't bad. However I would suggest a min 17' boat if your budget can swing it. The 16'ers typically don't have storage compartments if they do your life jackets and misc required boating equip take them up. So rods, tackle and reg gear will be left to be loose laying throughout bottom of boat. This can be a pain. Numerous road tip breaks or tripping over tackle boxes/coolers.
The one I had was rigged with 9.9hp kitted to 15hp. We had a great deal of 10hp below lakes back where I grew up in Southern Ill. I never hesitated to take it on big lakes either. (Kentucky Lake, Galveston Bay, Lake Texoma and various others). I would just have to pick my days and where I would launch.
One big factor to keep in mind is boat storage. Do you live in neighborhood where you will have to keep it in garage or pay for storage unit. This is the biggest limiting factor to me at the moment. I don't live in country anymore so I am limited to 20' of total boat length (back of motor to front of trailer). If you have to pay storage this can get pricey over time.
I am 50/50 on the Heritage. I think it is a good deal. Being brand new, you get the warranties and a little more peace of mind things shouldn't need fixed for a bit. However the upgrades I would want to do on the Heritage to be rigged like I would perfer would make it a $15k boat quickly. Like Fishnkamp mentioned try to stick to used. There are plenty of used rigs that come up for sale at good prices. And they will typically be rigged closer to what you would prefer at cheaper price or you will have room in budget to rig it as desired.