Learning to sew with a sewing machine is a journey ...
For the projects you mentioned something like a regular domestic machine would suffice. I've got a few projects I'm working on right now with my wife's Husqvarna Viking 6440 machine, vintage circa around 1980 or so. This was the top-of-the-line machine with all kinds of cams for fancy stitches that are not needed.
There are a couple really nice things about this machine, though:
1) The frame is a one-piece SOLID STEEL casting. Read: it doesn't move and will take just about anything that will fit under the presser foot.
2) The Vikings have had a low-gear ~ 10:1 for years. There are some old green Viking/Husqvarna machines from probably the late '40s or early '50s that use the low gear and one of these machines would do everything you want on the projects mentioned. My guess is one could be had really cheap.
The Viking is a "low shank" machine and will take all kinds of foot accessories that will help with various projects. There are "walking foot" attachments available. I've got one but haven't used it yet.
One project I just finished was a vinyl cover for our Avon, something to keep the sun, bird poop, and prying eyes off of. Currently I'm working on some covers for the running lights as the plan is to buy new ones then keep them looking like new and avoid sun crazing. The free-arm will be really good for that because it helps to be able to maneuver the material around while sewing. A flat-bed machine not so.
I'm also using Tenara thread, too. This stuff is really hard to work with, almost like sewing with fine wire. Wire that can really cause problems.
As for Tejas (and others comments), I'd agree with them. If we had the room and some more projets I'd go out and buy something like the high end Sailrite as this seems up my alley. However, I'm not quite there yet.
If one is really going to get into this sewing "business" (it can be addictive), it would be good to have two machines like a commercial-type flat-bed and something like the Viking free-arm. Each has it's place.
Adjustment and tuning: It really helps to know how a sewing machine works, if nothing else but to know when it's the one not working right. I've just started working with the Tenara thread and it's a challenge. It's not for everybody. Many in the canvas business won't touch it and a large Seattle canvas wholesale supply company won't even sell it.
For doing interior projects with regular (non-Tenara) thread, an old green Viking should do well. They came with zig-zag, a 10:1 low gear and a low-shank for attachments. The foot attachments can make a big difference in how it sews. A zig-zag foot has a relief underside to let the thread pass. A low-shank walking-foot attachment won't be as robust as on a machine with it built-in because it's an add-on but it can help. If you find you like these projects and want to expand the difficulty range then add another machine to the tool kit. This doesn't have to be an either/or decision, but more like a this-and-that.
Caution: not all "Vikings" are built with the robust solid steel cast arm. If it doesn't look like the early green machine or the somewhat newer 6440 type (do a search), then it may or may not be. Other brands that made some good domestics in years past include Pfaff and Bernina.
